Ernesto tried to determine the solution for the system of equations using substitution. his work is shown below.
x _ y = 7
3x _ 2y = 8
step 1: x = y + 7
step 2: 3(y + 7) _ 2y = 8
step 3: 3y + 7 _ 2y = 8
step 4: y + 7 = 8
step 5: y = 1
in which step did ernesto make the first error?
step 1
step 2
step 3
step 4

If m∠abc = 70°, what is m∠abd? justify your reasoning.  using the addition property of equality, 40 + 70 = 110, so m∠abd = 110°.  using the subtraction property of equality, 70 − 30 = 40, so m∠abd = 30°.  using the angle addition postulate, 40 + m∠abd = 70. so, m∠abd = 30° using the subtraction property of equality.  using the angle addition postulate, 40 + 70 = m∠abd. so, m∠abd = 110° using the addition property of equality.