4a + 6b=10

2a - 4b = 12

What is 12a

If you want to find the value of a, or of 12a, you'll need to eliminate the variable b. Try this: Multiply the first equation by 4 and the second by 6. You'll get 24b-24b=0. Solve for a. Then mult. a by 12, to obtain 12a and its numeric value.