To simplify this expression, we first need to combine like terms within the parentheses and then distribute the 5x to the resulting expression.

First, simplify the expression inside the parentheses:
3x - 2x - 15x(4-x)
= 3x - 2x - 60x + 15x^2
= x - 60x + 15x^2
= x - 60x + 15x^2

Now, distribute the 5x to the simplified expression:
5x(x - 60x + 15x^2)
= 5x^2 - 300x^2 + 75x^3

Finally, add 140 to the result:
5x^2 - 300x^2 + 75x^3 + 140

So, the simplified expression is:
75x^3 - 295x^2 + 140