A woman stands on flat ground at the base of a $90\text{-ft}$ observation tower. A hawk takes off from the top of the tower, descending at an angle of ${45}^{\circ }$ below the horizontal.

Write an expression for the angle of elevation $\theta$ from the woman to the hawk in terms of its current height $h$ above the ground. (Hint: The hawk has descended a vertical distance of $90-h$ from the top of the tower.)