College physics
posted by ali .
A student has built a 20cmlong pinhole camera for a science fair project. She wants to photograph the Washington Monument, which is 167 m (550 ft) tall, and to have the image on the film be 5.0 cm high.

Are not there two similar triangles here..from the pinhole enveloping the monument on one side, from the pinhole enveloping the image on the other.
Using similarity,
5cm/167m=.2m/d
solve for d, the distance to the Monument.
I think I did this problem in the 8th grade, it is odd seeing it again.