First, simplify the inequality by getting the x term with a coefficient of 1.
Divide both sides by -7. When you multiply or divide an equality by a negative number, you flip the inequality sign the opposite way.
-7x / -7 < -21 / -7
x > 3
In set build notation is would look like this: {x | x > 3}
Which would be read as "the set of all x, such that, x is greater than 3".
