help i'm really confused and i struggle with math

12.
4b - 6d
Replace the Variables(letters) with the numbers that it says the letters equal to.
4(7) - 6(3)
Multiple the numbers then subtract.
4(7)= 28
6(3)= 18
28 - 18 = 10
Evaluate the Expression means to Replace the Varaibles(letters) with the numbers it said it equals to.