The arrangement of mother's eye level, ground level and playground forms a right angles triangle.
The legs of this triangle are 12.6 m (eye level to ground) and 20 m (building to playground).
Using trigonometry and assuming the depression angle is Ф;
tan Ф = 20/12.6 = 1.5873
Ф = tan ^-1(1.5873) = 57.78°
As long as her speed was a constant, which according to this question she did, her speed would be about 5 mph(miles per hour)
The required equation is :
Now, let's find the required values :
[distance between any successive Crest or trough]
Distance of starting position from origin = k
Now, plug in the values ~