Solve for 'x':
[tex]\sf -3x+5<20[/tex]
Subtract 5 to both sides:
[tex]\sf -3x<15[/tex]
Divide -3 to both sides(be sure to switch the sign, we do this when multiplying/dividing by a negative number):
[tex]\sf x>-5[/tex]
So any number greater than -5 will be a solution.