In which line is an error first made when solving the equation below? -18=-9z-9
Line 1 2 = Z-9
Line 2 11 = Z
Line 3 Z = 11

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