Draw a diagram I choose a scale of 1:2 to fit better on the page
Draw a horizontal line. This is your base line. At it's mid point draw a vertical line running 2cm above and 2cm below your line. Put 2 dots on the horizontal line, one 3cm to the left of the vertical line and one 3cm to the right
Draw an arrow 1.5cm high vertically, 4.5cm from the lens line. This represents an arrow 3cm high, located 9cm from the lens but fits better on your paper.
Draw a horizontal line from the top of the arrow to the vertical lens line
Draw a second line from the top of the arrow through the mid point of the lens line, extending further out and also back towards the arrow because we don't know which side the image will be on. (or do we? maybe you already know)
Draw another line from the point where the horizontal line from the arrow touches the lens line, through the point 4.5 cm away from the lens line on the other side of the lens line to the arrow. extend it until it crosses the line you just drew.
Where these 2 lines cross is the tip of the image of the arrow. A real image is inverted and on the opposite side of the lens line to the arrow, and a virtual image is upright and on the same side as the arrow
Draw a line from this point down or up to the horizontal base line.
Measure the length of this line and multiply it by 2 to find the height of the image. Measure the distance from the lens line to the image and also multiply it by 2 to find the distance of the image from the lens
Comments
Draw a diagram I choose a scale of 1:2 to fit better on the page
Draw a horizontal line. This is your base line. At it's mid point draw a vertical line running 2cm above and 2cm below your line. Put 2 dots on the horizontal line, one 3cm to the left of the vertical line and one 3cm to the right
Draw an arrow 1.5cm high vertically, 4.5cm from the lens line. This represents an arrow 3cm high, located 9cm from the lens but fits better on your paper.
Draw a horizontal line from the top of the arrow to the vertical lens line
Draw a second line from the top of the arrow through the mid point of the lens line, extending further out and also back towards the arrow because we don't know which side the image will be on. (or do we? maybe you already know)
Draw another line from the point where the horizontal line from the arrow touches the lens line, through the point 4.5 cm away from the lens line on the other side of the lens line to the arrow. extend it until it crosses the line you just drew.
Where these 2 lines cross is the tip of the image of the arrow. A real image is inverted and on the opposite side of the lens line to the arrow, and a virtual image is upright and on the same side as the arrow
Draw a line from this point down or up to the horizontal base line.
Measure the length of this line and multiply it by 2 to find the height of the image. Measure the distance from the lens line to the image and also multiply it by 2 to find the distance of the image from the lens