Use Your Knowledge of English: 

1. Analyze the Units of the Answer. How many dimensions?

What is the density of water in lb/ft3, if the density of water at 25oC is 1.00 g/ml?    [Hint: There are 2.54 cm = 1 in (or 16.48 cm3 = 1 in3);
454 g = 1 lb ]

lb/ft3 is a density unit: which two dimensions (complex)!

2. Is there a two dimensional 'numbers and units' not connected to a Unit Factor in the problem?

"1.00 g/mL" is also a density unit of two dimensions
of Mass/unit Volume Given which can be connected to the Two Dimensional Density Unit of the Answer Unit Mass/Volume!

3. Equate the given to the unit asked for in the answer.

_???__ lb/ft3= 1.00 g/mL