12 The length of each side of regular pentagon ABCDE is represented by 3x + 1. Which
expression represents the perimeter of the
pentagon?
A. 3x + 5
B. 15x + 1
C. 18x + 6
D. 15x + 5

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