Yes, the formula is the place to start. The function f is 1 in the interval , and zero outside that interval. So the integral becomes , which you should be able to do.

Not sure about this, but I suspect that u(t) is meant to be the Heaviside function, defined by u(t) = 1 if t>0, and u(t) = 0 if t<0. If so then this function f(t) is zero when t<0, so the integral over negative values of t is going to be zero.