help needed changing words to formula for integration

Hey guys,

I know how to get the answer but I don't know what the formulas are (Worried)

The questions goes..

You start at rest on a bike. You accelerate at 1 m/s^2 for 4 seconds and then travel at a constant velocity until you arrive at your destination which is 80 metres from the starting position. Calculate travelling time.

I know I have to integrate twice to find the distance traveled during the acceleration period but I don't know what the formula for this question will be. I have a(t) = t ? But I don't get the correct answer when I integrate..

I can do the question in my head easy but we have to use integration.

Thanks