A rectangular water tank of base 11 m x 6 m

Given, dimensions of base of rectangular tank = 11 m x 6 m and height of water = 5 m

Volume of the water in rectangular tank = 11 x 6 x 5 = 330 m3

Also, given radius of the cylindrical tank = 3.5 m

Let height of water level in cylindrical tank be h.

Then, volume of the water in cylindrical tank $=\pi r^{2} h=\pi(3.5)^{2} \times h$

$=\frac{22}{7} \times 3.5 \times 3.5 \times h$

$=11.0 \times 3.5 \times h=38.5 \mathrm{hm}^{3}$

According to the question,

$330=38.5 h$ [since, volume of water is same in both tanks]

$\because$ $h=\frac{330}{38.5}=\frac{3300}{385}$

$\therefore$ $=8.57 \mathrm{~m}$ or $8.6 \mathrm{~m}$

Hence, the height of water level in cylindrical tank is 8.6 m.