I'm stuck with this problem - I can barely even understand what it says!

3. Let f(x) be a continuous function on the interval [a,b]. If

G(t) = (the integral from a to t) f(x) dx

for a<t<b*, show that G '(t) = f(t).

*these should actually be "equal to or less than" signs, but I don't know how to type mathematical signs on a forum.