The engineer can use a clinometer to measure the angle of elevation of the top of the tree. Let the height of the tree be represented by x, the she could determine the distance across the river, d, by applying the trigonometric function.
Tan θ =
=
the the distance, d = x ÷ Tan θ
Assume the angle of elevation of the top of the tree is , and the height of the tree is 10 m, then the distance, d, across the river would be;
d =
= 17.3190
d = 17.32 m
The sketch to the explanation is attached to this answer for more clarification.
One variable is the amount of days. Lets call the amount of days D. Another variable is the amount of pictures left. Lets call this p. In this case, since Emanuel is deleting 20 pictures a day, and he has 745 picture to start with, the equation would be 745- 20D=p.