The answer is 22.5 lb/gal.
The density of a liquid is quotient of mass and volume: D = m/V. The unit of the density is pound per gallon (lb/gal)
The density is unknown: D=?
But, we have:
mass: m= 90 lbs
volume: V = 4 gals
Do, the density of a liquid is:
D = 90 lbs / 4 gals
D = 22.5 lb/gal
