The charge that flows past a point depends on the current and on how long it flows. For a steady current, charge = current × time, or Q = I × t. Charge Q is in coulombs (C), current I is in amps (A) and time t is in seconds (s). So one amp is a flow of one coulomb each second.
For example, a current of 3 A for 10 s moves 3 × 10 = 30 C of charge. The equation can be rearranged: I = Q / t and t = Q / I. If 40 C flows in 8 s, the current is 40 / 8 = 5 A.
The time must always be in seconds, and there are 60 seconds in a minute. A current of 0.4 A for 3 minutes is 180 s, so the charge is 0.4 × 180 = 72 C. A common mistake is to use 3 for the time instead of 180.