Stoke's law states that the viscous drag force $F$ experienced by a sphere of radius $a$, moving with a speed $V$ through a fluid with coefficient of viscosity $\eta$, is given by $F = 6\pi\eta a V$. If this fluid is flowing through a cylindrical pipe of radius $r$, length $l$ and a pressure difference of $P$ across its two ends, then the volume of water $V$ which flows through the pipe in time $t$ can be written as $V = k\left(\frac{P}{l}\right)^a \eta^b r^c$, where $k$ is a dimensional constant. Correct values of $a$, $b$ and $c$ are