Start with
[tex] -2x-4 < 3x+21 [/tex]
Add 2x to both sides:
[tex] -4 < 5x+21 [/tex]
Subtract 21 from both sides:
[tex] -25 < 5x [/tex]
Divide both sides by 5. Since it is positive, we don't have to change the inequality sign:
[tex] -5 < x [/tex]
So, the answer is [tex] x > -5 [/tex]
