When an External Resistor of Resistance $R _ { 1 } = 14 \Omega$

When an external resistor of resistance $R _ { 1 } = 14 \Omega$ is connected across the terminals of a battery, a current of $6.0 \mathrm {~A}$ flows through the resistor. When a different external resistor of resistance $R _ { 2 } = 64.4 \Omega$ is connected instead, the current is $2.0 \mathrm {~A}$ . Calculate (a) the emf of the battery and (b) the internal resistance of the battery.