Every day on Tim's walk to school he comes to a river. He has to walk far out of his way to find a shallow crossing point. Tim would like to construct a bridge across the river to shorten his walk to school. He finds that the point at which he cross the river is 2 miles away and that he makes a 60 degree turn to get back on his path to school. Given that the angle formed by the bridge and Tim's path after crossing the river will be 70 degrees, as shown in the diagram below, can you help Tim figure out how long of a bridge he would need to construct?

The slider tool allows you to change the angle at the point where Tim crosses the river.
a) Use the slider tool to help you estimate the length of Tim's bridge. Justify your estimate.
b) Is there a relationship between an interior angle of a triangle and the side opposite that angle? Explain.