Correct option is (c) 72.8%
Volume = πr2h
new radius = r + \(\frac{20}{100}\)r
= \(\frac 56\)r
So
\(= h + \frac{20}{100}h\)
\(= \frac 65 h\)
Volume = π\(\left(\frac {6r}5\right)^2 \left(\frac 65h\right)\)
\(= \frac{216}{125} \pi r^2 h\)
∴ Increase in volume = \( \frac{216}{125} \pi r^2 h\)