A student has built a 20-cm-long 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.

Answer 1

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.

Answer 2

668m