Each ounce of yogurt costs $0.12 so 8 ounces would be $0.96
Substitute 6 - 2x for y in the first equation
3x - (6 - 2x) = 4
5x - 6 = 4
5x = 10
x = 2
Plug 5 for x in either equations (I'll use the second equation)
y = 6 - 2 * 2
y = 6 - 4
y = 2
(2,2) is the solution.