To solve this problem you must apply the proccedure shown below:
 1. You have the following information given in the problem above:
 - The tree is 100 feet tall.
 - The tree casts a shadow that is 150 feet long.
 2. Therefore, you have:
 Tan^-1(α)=opposite/adjacent
 Where:
 - α is the angle.
 - opposite=100 feet.
 -adjacent=150 feet.
 2. When you substitute these values, you obtain:
 Tan^-1(α)=100/150
 α=34º
 The answer is: 34º