Help! I’ll mark brainlest :) asap

Thales was an ancient philosopher familiar with similar triangles. one story about him says that he found the height of a pyramid by measuring its shadow and his own shadow at the same time. if the person is 5-ft tall, what is the height of the pyramid in the drawing?

How is working backward similar to solving an equation?

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)