When you need to change units you need to know the realtionship between those units:
You need to use six unit multipliers, it means you need to know the relation between each unit you use.
As miles is a unit to distance, you can use the next units:
Miles to kilometer: 1 mile is equal to 1.61km
kilometer to meter: 1km is equal to 1000m
meter to yard: 1 meter is equal to 1.09361yd
yard to centimeter: 1yd is equal to 91.44cm
centimeter to feet: 1 ft is equal to 30.48cm
feet to inches: 1 ft is equal to 12 inches
Then you get:
[tex]30miles^3\cdot\frac{1.61\operatorname{km}}{1miles^3}\cdot\frac{1000m^3}{1\operatorname{km}}\cdot\frac{1.09361yd^3}{1m^3}\cdot\frac{91.44\operatorname{cm}}{1yd^3}\cdot\frac{1ft^3}{30.48\operatorname{cm}}\cdot\frac{12in^3}{1ft^3}[/tex][tex]=1901569.068in^3[/tex]