Hi,
Part of the solution will involve finding the response of the capacitor to the current source of 5 amps with the appropriate resistor value in parallel when the source of 100 volts is shorted out. So see if you can first calculate the voltage response of a capacitor in parallel with a resistor driven by a parallel current source. So you have three things in parallel: A resistor, a current source, and a capacitor. If you can find the response to this (perhaps use Thevenin and/or Norton) you're well on your way to solving this problem in the manner in which you desire. This solution involves superposition too.