1) 4a + 7b = 5
2) 8a - 3c = 36
3) 6b - 3c = 6
subtract eq(3) from eq(2):
8a - 3c = 36
6b - 3c = 6
__________
8a - 6b = 30 (a)
multiply eq(1) by 2, subtract from eq(a):
8a - 6b = 30
8a + 14b = 10
_____________
-20b = 20
b = -1
using eq(1):
4a + 7(-1) = 5
4a = 12
a = 12/4 = 3
using eq(2):
8(3) - 3c = 36
-3c = 12
c = -12/3 = -4
a = 3, b = -1, c = -4
You can check these by plugging the values into eqs 1 - 3