How many milliliters of a substance with a specific gravity of 0.88 would be needed to have 0.75 pounds of it?
0.88 what? g/mL; lb/cubic foot; kg/L; tons/gallon? I'll assume you mean 0.88 g/mL.
0.75 lb x 453.6 g/lb = z grams
Then 0.88 g/mL x ?mL = z grams from above.
Solve for ?mL.