How do you do this calculus problem? #2?

A point Q1 moves along the positive x-axis with a constant velocity -20 m/s. A point Q2 moves along the positive y-axis with a constant velocity +10 m/s. At time t, the line segment Q1Q2 makes an angle of H(t) at Q1, measured clockwise from the x-axis to the line segment (so that 0