A jet of water having a velocity of $20 \mathrm{~m} / \mathrm{s}$ strikes a series of plates fixed radially on a wheel revolving in the same direction as the jet at $15 \mathrm{~m} / \mathrm{s}.$ What is the percentage efficiency of the plates? (round off to one decimal place)
- $37.5 $
- $66.7$
- $50.0$
- $88.9$