y = 3x - 5
So substitute 3x-5 for y:
6x + 3(3x-5) = 15
Simplify:
6x + 9x - 15 = 15
15x - 15 = 15
x - 15 = 1
x = 16
THEN find y by plugging the value of x back into the first equation:
y = 3(16) - 5
y = 48 - 5
y = 43
