you have two equations
3x + 6y = 69 ...(1)
2x - y = 11 ...(2)
we're going to use simultaneous equations to cancel out x and find y
first, multiply (1) by 2:
6x + 12y = 138 ...(3)
multiply (2) by 3:
6x - 3y = 33 ...(4)
then we subtract equation (4) from (3)
[(6x-6x) + (12y - -3y) = 138 - 33]
15y = 105
y = 7
hope that helped :)