-138 ≥ -6(6b - 7)
Start by multiplying everything within the parentheses by -6.
-138 ≥ -36b + 42
Now move the +42 to the other side, so you're left with -36b. (You do this by subtracting 4242)
-138 - 42 ≥ -36b
-180 ≥ -36b
Divide both sides by -36 to find the value of b.
-180 / -36 ≥ b
5 ≥ b.
The answer is b ≤ 5.