The rate (in liters per minute) at which water drains from a tank is recorded at half-minute intervals. Use the average of the left- and right-endpoint approximations to estimate the total amount of water drained during the first 3 min.

$t$ min	0	0.5	1	1.5	2	2.5	3
l/min	44	42	40	38	36	34	32

Answer: liters.