The ratio diameter to heigth of a can of tuna is 3 : 2
Given that the water tank has a similar shape, its ratio diameter to heigth is the same. Then:
Diameter/height = 3/2
Replacing with Diameter = 30 yards, we get:
30/height = 3/2
30*2/3 = height
20 yards = height
1 yard is equivalent to 36 inches, then 20 yards is equivalent to 20*36 = 720 inches