Your answer can be derived from an understanding of the unit of current. In your problem, 0.2 A of current is flowing. (We'll assume that this value remains unchanged for the duration of the experiment. In practice this is rarely the case when one is speaking of accumulated current, for example in a capacitor.)

The unit of current is the Ampere (A, or Amp). The definition of the Ampere is 1 C / s (1 Coulomb/second). So, to get the amount of charge that has traveled past a specific point (or accumulated), multiply the current by the time:

Charge ( in Coulombs) = Coulombs / second x #seconds

Or, for your problem statement,

460 mC = 460 x10-3 Coulombs = 0.2 Coulombs / second x T seconds

Solve for T:

**T = 0.460 C / 0.2 A = 2.3 seconds **