I would say it's the one you have checked off on the paper.
7x1=7, then 4x1/4= 4x1=4 divided by 4= 1. Then subtract 7- 1= 6
Density = mass/volume
volume cube = side^3 = 5^3 = 125 cm^3, don't forget units!
Density = 250 grams / 125 cm^3 = 2 g/cm^3, with all the units