b$)$ A centrifugal pump has a $200mm$ diameter suction pipe and a $150mm$ diameter delivery pipe. When discharging $30\frac{l}{s}$ of water, the inlet water mercury manometer with one limb exposed to the atmosphere recorded a vacuum deflection of $198mm$; the mercury level on the suction side was $120mm$ below the pipe centreline. The delivery pressure gauge, $220mm$ above the pump inlet, recorded a pressure of $\frac{0\mathrm{.}95}{b}ar.$ The measured in put power was $3\mathrm{.}2kW.$ Calculate the pump efficiency.

$[12]$