His sister is 4 feet tall. Her shadow is 7 feet long. From the top of her head to her shadow, how long is it? (Nearest tenth of a foot)

For this problem you need to use the Pythagorean theorem. The adjacent side to the right angle is the 4 feet and the opposite side is 7 feet.

4^2 + 7^2 = x^2

16 + 49 = x^2

65 = x^2 = > 8.06225 ... So the distance is 8.1 feet to from the top of her head to the shadow.