Six more than five times a number is at least twenty one is set up like this:
6 + 5x ≥ 21
By subtracting six from both sides you're left with 5x ≥ 15
Divide five from both sides to isolate the variable and you're done.
x ≥ 3 (By being greater or equal to three x can be 3, 4, 5, 6, etc.)