Well if the rest of the equation looks like this
{4a+6b=10, 2a-4b=12}
Solve for 'a' in equation 2
2a-4b=12
2a=12+4b
a=6+2b
Substitute (6+2b) for 'a' in equation 10
4a+6b=10
4(6+2b)+6b=10
24+8b+6b=10
24+14b=10
14b=-14
b=-1
Substitute (-1) for 'b' in equation 2
2a-4b=12
2a-4(-1)=12
2a+4=12
2a=8
a=4
{a=4, b=-1}
--> 12a=48
