Question

A water canal has a rectangular cross section 4 meters wide and 3 meters deep. How much water is contained in a 20 meter length of the canal? How much water will be held after 40% has evaporated?

Answer 1

For part a)
This is asking forth volume:
V = l*e*h
V = (4)(3)(20)
V = 240 m^3

for b) if 40% evaporates, you are left with 60% of the water:
60/100* 240
= 144 m^3