Answer:
height temple (other bank) = 54
Width of river = 31.177
Step-by-step explanation:
What you get is something that resembles a rectangle. That's because the two angles of depression add to 90 degrees. Therefore from the top of the given temple to the one across the river add up to 90 and the temples are both perpendicular to the ground.
So the other temple is 54 m high as well.
Now for the width of the river. The width of the river is the opposite side making up the tan(30) degree angle.
Formula
Tan(30) = river width/ height of first temple.
Tan(30) = river width / 54 m
Tan(30) = 0.5774
0.5774= river width / 54 Multiply both sides by 54
0.5774*54 = river width
river width = 31.177