Which trigonometric identity you can use here and how many unknown lengths you have to find out to get the final answer?

Cos theta is the ratio of which two sides?

Use the height and distance rules.

Use the concept of angle of elevation then use this trigonometric concept tanθ = perpendicular/base

Which trigonometric identity you can use here and how many unknown lengths you have to find out to get the final answer?

Which trigonometric identity you can use here?

Which trigonometric identity you can use here?

Let width of river= x+y metres

tan60° =

So we get, x=

and, tan45°=

So we get, y=100

Width of river= x+y= 157.7 metres

Height of tower = height of building + remaining height

remaining height can be calculated by using the tanθ trigonometric identity