Water flows into a storage tank at a rate R(t) (in liters per minute) recorded at the times below.
t (min): 0 1 3 5 7
R(t) (L/min): 2.0 3.0 3.5 4.0 3.0
Assuming the rate changes linearly between the recorded times, determine the total volume of water, in liters, that enters the tank during the first 7 minutes.