Stuck on some problems again (Thinking)

A car starts from rest and moves in a straight line. After t seconds, its acceleration, a m s^2 is given by a=(0.2)(18t). Find the distance travelled in the first 30 s given that the speed of the car at t=30 is 18m/s.
I tried to integrate a twice to get S but I can't get the answer of 720m.
Am i doing anything wrong or missing out anything?

A particle, travelling in a straight line, passes a fixed point O on the line with a speed of 0.5 m/s. The acceleration, a m/s^2 , of the partiicle , t seconds after passing O, is given by a = 1.40.6t
Find the total distance travelled by the particle between t = 0 and t = 10
For this I have tried to do the same as the above
and i figured that S = 0 when t = 0(since t starts increasing after particle passes O) so C = 0.
Then i found S at t=5(where it comes to inst. rest) to be 1.25m and S at t=10 to be 75m but doing the math it comes nowhere near the answer of 40m.
I appreciate any inputs (Wink)