A level Physics Capacitance question (1)

Thank you so much for helping I think I get it but if RC=1 so R = 1/(470 x 10^-6 ) = 2127 but that isn't a option where did I go wrong ?

Can someone please explain how I am meant to solve this I have no idea where to start ?

You have misunderstood the hint provided by Joinedup:
“in an elapsed time of 1 time constant the PD will be reduced to 37% of V₀ (because e^-1 is 0.3679)”
You need to go to the graph to find the time for 1 time constant and 1 time constant is NOT EQUAL TO 1 in this case.
1 time constant is the time elapsed for the voltage to drop from the initial voltage V0 to 0.3679 of the initial voltage, 0.3679V0.
Once you have found the time elapsed say T, you will solve Eq 1:
$\dfrac{T}{RC} = 1$ ---Eq1
This is easier to solve.
If not, you can use the discharge voltage formula given by Joinedup to attempt the question:
$V = V_0 \exp(-t/RC)$ ---- Eq2
Solving Eq2 is more tiresome than Eq 1.