The rain which falls on a roof 18 m long and 16.5 m wide is allowed to be stored in a cylindrical tank 8 m in diameter.

Length of the water on a roof = 18 m

Breadth of the water on a roof = 16.5 m

Height of the water on a roof = 10 cm=0.1 m

Volume of the water on a roof $=$ Length $\times$ Breadth $\times$ Height $=18 \mathrm{~m} \times 16.5 \mathrm{~m} \times 0.1 \mathrm{~m}=29.7 \mathrm{~m}^{3}$

Since water is to be stored in the cylindrical tank, the volume of water on a roof is equal to the volume of a cylindrical tank.

Volume of cylindrical tank = πr2h = 29.7 m3

$h=\frac{29.7}{\frac{22}{7} \times(4)^{2}}=0.5906 \mathrm{~m}=59.06 \mathrm{~cm}$

Thus, the rise of water level in the tank is 59.06 cm.