What is this

{x+y=12

0.99x+1.15y=12.52

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