The Author of this book does not really explain the process very thoroughly, consequently I am lost.

$\displaystyle \frac{72x}{18xy}$

to solve:

$\displaystyle \frac{4}{y} * \frac{18x}{18x} = \frac{4}{y}$

I am completely stumped as to how the author gets $\displaystyle \frac{4}{y} $ and$\displaystyle \frac{18x}{18x}$, if someone could please clarify and tell me the process, and why its implemented it would be greatly appreciated.

When I look at it I dont see why you cant just cancel out the x in the numerator and denominator and get $\displaystyle \frac{72}{18y} = \frac{4}{y} $ I dont understand how she sets it up at all.