Simple
Nine less than a number times four equals fifteen
basically, x*4-9=15 would be your equation, or something similar
Well, we know x can't equal 1,2,3,OR 4. Five is also out, because 5*4=20-9=11, so cross that out.
But if you try doing 6*4-6=15, it fits.
6*4=24, 24-9=15
Thus, x=6, so your answer to Nice less than four times a number equals fifteen is 6.
~Hope this helps!