Calculation ilaplace ...roots? plot

Hello,

I need make inverse Laplace transformation. I thing I got more roots. What can I do with this roots? I need make plot "a". How can I do that? Calculation of "a" in command window is fast, but in guide it takes so long time .

a=ilaplace(-(561000*2^(1/2)*s^3 + (56100000*2^(1/2) + 176154000*6^(1/2))*s^2 + (340000*2^(1/2) + 17615400000*6^(1/2))*s + 106760000*6^(1/2))/((s^2 + 98596)*(231*s^3 + 79200*s^2 + 3961040*s + 64000)))

a =

(5651520641074021412265585573*cos(314*t))/804286799586829234264342528 - (3844933080772282316677803810547*sin(314*t))/252546055070264379559003553792 + (90644313328981118471354502927*sum(exp(r10*t)/(693*r10^2 + 158400*r10 + 3961040), r10 in RootOf(s10^3 + (2400*s10^2)/7 + (3961040*s10)/231 + 64000/231, s10)))/201071699896707308566085632 - (49380243605538013116805873912193*sum((r10*exp(r10*t))/(693*r10^2 + 158400*r10 + 3961040), r10 in RootOf(s10^3 + (2400*s10^2)/7 + (3961040*s10)/231 + 64000/231, s10)))/201071699896707308566085632 - (1305501268088098946233350267363*sum((r10^2*exp(r10*t))/(693*r10^2 + 158400*r10 + 3961040), r10 in RootOf(s10^3 + (2400*s10^2)/7 + (3961040*s10)/231 + 64000/231, s10)))/804286799586829234264342528