General

help in physics required S

Hi basilers,

I am stuck on this question and have no idea why this is the answer or how to get to it.

A particle having a charge of q = 2.5 * 10^-8 C has an instantaneous velocity of v = -3.0 * 10^4 i + 5 * 10^4 j m/s and moves in a region where the magnetic field is B = 2 i T. What is the force of the particle?

I know we're supposed to use F = q v cross b, but idk how to do that :S. Can someone show me the solution the this problem? The answer is apparently F = -2.5 k mN.