Can someone help me on this question it need to be done to day?!

What is the difference between the predicted value and the actual value

From the top of a tree a bird looks down on a field mouse at an angle of depression of 50°. if the field mouse is 40 meters from the base of the tree, find the vertical distance from the ground to the bird's eyes.

Solve the equation for b: a= (1/2)(b)(h)