I don't get these why are they so hard???

1) For the following masses and volumes calculate the density in g/cm3.

a) 452.1g and 392cm3

b) 0.14lb and 125 ml

c) 1.01kg and 1000cm3

d) 225mg and 2.51ml

2) Calculate the density of 784.6g of acetone with a volume of 1000ml .

3) Perform the following conversions showing the conversion factors used.

a) 8.43cm to mm

b) 2.41x10^2cm to m

c) 294.5nm to cm

d) 404.5m to km

4) Perform the following conversions showing the conversion factors used.

a) 908oz to kg

b) 12.8l to gallon

c) 125ml to quarts

I don't get these why are they so hard???getting late

1)

a) 4521g/392cm3 = 1.15 g/cm3

b) (0.14lb x 1000g/2.2lb)/125cm = 0.51 g/cm3

c) 1010g/1000cm3 = 1.01 g/cm3

d) 0.225g/2.51cm3 = 0.0896 g/cm3

2) 784.6g/1000cm3 = 0.784 g/cm3

3)

a) 8.43cm x 10mm/1cm = 84.3 mm

b) 2.41x10^2cm x 1m/100cm = 2.41 m

4)

a) 908oz x 1lb/16oz x 1kg/2.2lb = 25.8 kg

b) 12.8L x 0.264gal/1L = 3.38 gal

c) 125mL x 1L/1000mL x 0.264gal/1L x 4qt/1gal = 0.132 qt