First, determine what the integral is for :
Did you get that? Note that I used a lower-case f to denote the original function, and capital F to denote the integral. Next, evaluate F(x) at the point x=4, and subtract the value at x = 1:
Note that the constant C cancels out. Since the constant of integration always cancels when evaluating definite integrals, most people simply don't bother including it in their work, but I think it's good practice to not forget about it. Hope this helps!