3a + 4c = 80
2a + 3c = 57
How can we cancel something out?
-2(3a + 4c = 80)
3(2a + 3c = 57)
-6a - 8c = -160
6a + 9c = 171
Adding these together...
c = 11
3a + 4(11) = 80
3a + 44 = 80
3a = 36
a = 12
Hope this helps!