A battery of $10 \mathrm{V}$ is connected to a resistance of $20 \mathrm{\Omega }$ through a variable resistance $\mathrm{R}$. If the variable resistance $\mathrm{R}$ is increased at the rate of $5 \mathrm{\Omega } {\min }^{-1}$, then the amount of charge that passes through the battery in $4 \min$ is