Question 1015304
Systems of equations: Subsitution method.

2x+6.50y=120.50
x+y=31

To know what x is equal to, change the second equation to x=31-y.

Now, substitute 31-y for x in the first equation 2(31-y)+6.50y=120.50.
Solve: 62-2y+6.50y=120.50.
62+4.50y=120.50.
120.50-62=38.50.
4.50y/4.50=58.50/4.50
y=13. 
Now substitute 13, which is y, into x=31-y 
X=31-13
x=18. 
The solution is (18,13) (x,y). 

I hope this helped.