Eduardo solved the following inequality, and his work is shown below:

−5(x + 4) + 21 ≥ −3 + 4(x − 8)
−5x − 20 + 21 ≥ −3 + 4x − 32
−5x + 1 ≥ 4x − 35
−9x ≥ −36
x ≥ 4

a) when dividing by −9, he did not change the ≥ to ≤.
b) he subtracted 4x from both sides when he should have added 5x.
c) he subtracted 1 from both sides when he should have added 36.
d) he did not make a mistake.