I'm not sure how to do these two questions. Any help with both or one is appreciated!!

1) A balloon rises into the air started at point P. AN observer, 100m from P looks at the balloon and the angle theta between her line of sight and the ground increases at a rate of 1/20 rads per second. Find the velocity of the balloon where theta = pi/4

The answer is 10m/s I'm just not sure how to get it.

2) One end of a ladder of length 5m slides down a verticle wall. When the upper end of the ladder is 3m from the ground, it has a downward velocity of 0.5m/s. Find the rate at which the angle of elevation is changing at that time.

Again, the answer is 0.125 rad/s