so, we'll first convert the mixed fraction to "improper", and then sum both widths and lengths to get the perimeter.
[tex]\bf \stackrel{mixed}{4\frac{3}{4}}\implies \cfrac{4\cdot 4+3}{4}\implies \stackrel{improper}{\cfrac{19}{4}}\\\\
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\textit{then the perimeter will be the sum of widths and the lengths}
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\cfrac{19}{4}+\cfrac{19}{4}+6+6\implies \cfrac{38}{4}+12\implies \cfrac{19}{2}+12\implies 9\frac{1}{2}+12\implies 21\frac{1}{2}[/tex]
