Find the displacement with an increasing acceleration? The actual question is below.

A particle #P# travels in a straight line.

At time #ts#, the displacement of #P# from a point #O# on the line is #sm#. At #ts#, the acceleration of #P# is #(12t-4)ms^-2#. When #t=1#, #s=2# and when #t=3#, #s=30#.

Find the displacement when #t=2#.

Okay, so that's the question. From this I can get the acceleration by inputting the #t# into the equation for acceleration:
#a=12t-4=12(2)-4=24-4=20ms^-2#
After this, how would I get to the answer?
Would I need to integrate once to get the velocity (in terms of c)? // When I integrate I get #12t^2-4t+c=v# but how would I find c?