A fully charged 7.7 capacitor is connected in series with a 2.0×10^{5} resistor. What percentage of the original charge is left on the capacitor after 1.8 of discharging?

I know the formulas to use are i(t)=I_0*e^(-t/RC) and q(t)=C*emf*e^(-t/RC)

Don't know where to start....