(Solved): The circuit schematic below consists of a battery whose mf=15V and has an unknown internal resi ...

The circuit schematic below consists of a battery whose $?mf=15\mathrm{V}$ and has an unknown internal resistance, $r$. When the battery is connected to a resistance, $R$, the terminal voltage (the voltage across the battery or points $a$ and $b$ on the schematic) drops to $13.5\mathrm{V}$ and the current in the circuit is measured to be 1.5A. Determine the value of the resistance $R$ and the internal resistance, $r$, of the battery.