Finding the voltage and current at t = 0 using Step Response
Homework guidance:
Nobody shorts the 1 Ohm resistor, its end is opened so its current is stopped at t=0. Before t=0 there were 4A as your voltage division shows.
At t=0 the circuit changes. You have 4V in the capacitor, 20V in the source and a resistor between. The capacitor charges towards 20V starting from 4V. Find the formulas.