Find the value of X and Y

Witch represents the inverse of the function f(x)=1/4x-12

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

1. ∠1 is complementary to ∠2 and ∠3 is complementary to ∠2. subtraction property of equality 2. m∠1 + m∠2 = 90 and m∠3 + m∠2 = 90 substitution 3. m∠1 + m∠2 = m∠3 + m∠2 definition of complementary 4. m∠1 = m∠3 given