I don't fully understand how to do these types of questions and I need help on how to get the answer.

You need to know some formulae, that's all.

Here, you need to know:
P = IV

Use the values given:

12 = 120I

Find I now. :)

From V=IR and P=VI you can derive all of the formulas needed.

Example:

You can substitute V=IR for P=VI and get P = I*R*I or P=I^2(R)

You need two out of the 4 (P, I, V, R) quantities to solve for any other one. You need to know P=VI and V=IR and can derive the rest.

You also must use the correct units of Watts, Amps, Ohms and Volts.