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For convenience write RC=D and solve the ODE dV/dt=-V/D which gives
V=Ae^(-t/D) by separating the variables.
When t=0, V=10 and this gives A=10,
when t=2, V=1 giving 1=10e^(-2/D) and you can find D by taking lns of
each side. D=RC, so R=D/C
You should get 2.90X10^5 ohms