Solve each system of equations by using either substitution or elimination. 10m - 9n = 15 5m - 4n = 10 a. (6, 5) c. (4, -3) b. (-8, -3) d. no solution Please select the best answer from the choices provided A B C D

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