The second equation equals: 3X +18y=60 (Both sides times 3)
And then use this new equation minus the first equation, you will get:
Left side: (3X +18y) - (3x+6y)
Right side: 60-30
So 12y=30
Then y=2.5
Take y value into one of the three equations, you will get x=5
or
in another easier way:
Directly minus the second equation from the first one:
(3x+6y) -(X+6y)=10
2X = 10
X = 5
Get Y is easy, Y=2.5