Volume of cylinder = pi*r^2*h
given that D=14 so R=7 and h=14inches

Hose A
in 1 minute fills one gallon
in 1.5 minutes fills 1.5 gallons

Hose B
in 1 minute fills 1.5 gallons
in 1.5 minutes fills 2.25 gallons

After 1.5 minutes the total volume of water filled in the pail is 3.75 gallons

Now the portion of the cylinder filled with water can be considered a new cylinder
having volume =3.75 gallons h=? and r=7 inches (as the base stays the same for both cylinders)
Converting volume from gallons to cubic inches we get volume =3.75*231 cu.inches


Substituting these values in the formula

Volume of cylinder = pi*r^2*h

we get

3.75*231=(pi)(7^2)(h)
h=(3.75*231)/(pi*49)
h=5.6

Hence D