how can i use laplace initial value problem with step function for the given example?

for example: D^3x-Dx= 1 for t<2 =0 for t >=2 having x(o)=x'(0)=x''(0)=0

I know the basic of laplace in matlab like using syms t s x and using dsolve method to solve but dont know how to write this togther with step function to get final answer..