let,
x+y=12. be 1. and
0.99x+1.15y=12.52 be 2
multiply 1 by -0.99
therefore
-0.99x-0.99y=-11.88
no
w let this equation be 3
and now
add equation 2 and 3
0.99x-0.99x+1.15y-0.99y=12.52-11.88
therefore 0.16y=0.64
therefore y = 0.64/0.16
therefore y=4
now put y=4 in equation 1
x+4=12
therefore
x=12-4
therefore
x=8
