Fatima has 3 packs of batteries. Each pack contains 4 batteries. She gives her brother 8 batteries to put in his toy robot.

Let b represent the number of batteries Fatima has left.

Which equation could be used to find the value of b?

a. 3 + 4 + 8 = b

b. 3+4−8=b

c. 3 × 4 + 8 = b

d. 3×4−8=b