Could anyone explain? Thank you.

Question 5 Not answered Marked out of 1.00 Flag question A village wishes to measure the volume of water that is piped to a factory during one afternoon. The graph below shows the flow rate r (in cubic meters per hour) at any time in this afternoon. Estimate the total volume of water (in cubic meters) used by the factory between 12 am (t = 0) and 7 pm (1 = 7). Ar (m3/ hr) 50 40 30 20 10 0 1 2 3 4 5 6 7 t (hr)