let's firstly convert the mixed fraction to improper fraction.
[tex]\bf \stackrel{mixed}{3\frac{1}{2}}\implies \cfrac{3\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{7}{2}} \\\\[-0.35em] ~\dotfill\\\\ \left( -\cfrac{7}{2} \right)^2\implies \left( -\cfrac{7}{2} \right)\left( -\cfrac{7}{2} \right)\implies \left( \cfrac{7^2}{2^2} \right)\implies \cfrac{49}{4}\implies 12\frac{1}{4}[/tex]
