algebra

2x + 6y = 66
8x - y = 39

x = (66 -6y) / 2
8x - y = 39

x = 6 * (11 - y) / 2
8x - y = 39

x = 3 * (11 - y)
8x - y = 39

x = 3 * (11 - y)
8*(3 * (11 - y)) - y = 39

x = 3 * (11 - y)
264 - 24y - y = 39

x = 3 * (11 - y)
- 25y = 39 - 264

x = 3 * (11 - y)
- 25y = -225

x = 3 * (11 - y)
y = 9

y = 9
x = 3 * (11 -9) =6

[input]solve( 2x + 6y = 66, 8x - y = 39 )[/input]