the area, assuming is a rectangular floor, is their product.
so simply convert the mixed to improper and get their product.
[tex]\bf \stackrel{mixed}{100\frac{3}{4}}\implies \cfrac{100\cdot 4+3}{4}\implies \stackrel{improper}{\cfrac{403}{4}}
\\\\\\
\stackrel{mixed}{75\frac{1}{2}}\implies \cfrac{75\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{151}{2}}\\\\
-------------------------------\\\\
\cfrac{403}{4}\cdot \cfrac{151}{2}\implies \cfrac{403\cdot 151}{4\cdot 2}\implies \cfrac{60853}{8}\implies 7606\frac{5}{8}~ft^2[/tex]
