Im not sure how to solve the system?

so... first off, let arrange the variables, so they align vertically

thus    

now.. let's try say.. elimination method

alrite, let's hose the "x"'s

so... we have a -8x atop and a 7/18x at the bottom, what the dickens can we multiply 7/18 so we can end up with with a positive 8?   that way it becomes 8x and -8x + 8x = 0, effectively hosing the "x"s

hmm ok.. let's say... we need to multiply the 7/18 by "a".. .let's find out what "a" is then   

low and behold, if we multiply then, 7/18 by 144/7, we end up with "8"
so let's do that for the 2nd equation then



alrite.. so..now we know  y = -6, let us use that in the first equation then

The correct answer is addition