convert to cubic feet:
64.2 inches x 30.0 inches x 26.0 inches
u can do that $\displaystyle \frac{64.2in}{1} *\frac{1ft}{12in}$ and that would cancel inches out blah blah....then repeaton on other 2 dimensions then multiply to geth ur answer in feet cubed
however this may also help u in the future $\displaystyle \frac{1ft^3}{1}*\frac{12in}{1ft}*\frac{12in}{1ft}* \frac{12in}{1ft} $thus canceling feet cubed so you now have $\displaystyle 1ft^3= 1728in^3$
thus $\displaystyle 64.2in*30.0in*26.0in =50076in^3 * \frac{1ft^3}{1728in^3}$giving you $\displaystyle 28.979...ft^3$
we can check your answer by doing the above method chris showed (probobly safer but much much slower.....(as u can record how man inches cubed are in a feet for future use)
so $\displaystyle \frac{64.2in}{1}\frac{1ft}{12in}=5.35ft$
$\displaystyle \frac{30in}{1}\frac{1ft}{12in}=2.5ft$
$\displaystyle \frac{26in}{1}\frac{1ft}{12in}=2.1111...ft$
and finaly
$\displaystyle 5.35ft*2.5ft*2.1111..ft=28.979...ft^3$
hope that gives u help in the future..shortcuts are always nice(just can get messy if u make mistakes)