21 is greater than or equal to 3 (a-7) + 9

21≥ 3 (a-7) + 9

first, just solve it like a normal equation

Distribute

21 ≥3a-21+9

Combine numbers

21 ≥3a-12

Solve like equation

33 ≥3a

11≥a

"a" has to be less than or equal to 11 for the inequality to be true