Similar and Congruent Figures Question

Anne is trying to determine the width of a river that flows from east to west. She is currently standing on the south side of the river, very near the river's edge. Directly across the river, almost touching the water, is a large tree. She knows that she can create two similar triangles to measure the width of the river. She begins walking due west for 21 ft, and then walks 10 ft south. Looking directly at the large tree she noticed earlier across the river, she walks towards the river in a north-easterly direction. When she arrives at the river, she sees that she is exactly 14 ft west of her original starting point. How wide is the river at the point from which she was originally standing? Round the answer to one decimal place if necessary.

1. 20 ft
2. 15 ft
3. 9.8 ft
4. 6.7 ft