b) 75 acres to square meter
Consider that 1 acre = 4046.86m^2:

c) 4637 nm^3 to in^3
First, consider that:
1 nm = 10^-9 m
1 m = 39.3701 in
then, you have:

by powering to 3, you obtain:

Then, for the given quantity, you obtain:

c) 71.63 g/cm^3 to mg/dm^3
In this case, use two conversion factor for mass and volume in the same procedure, as follow:
![71.63\frac{g}{\operatorname{cm}^3}\cdot(1000mg)/(1g)\cdot\frac{1dm^3}{1000\operatorname{cm}^3}=71.63(mg)/(dm^3)]()