one hour is half of 2 hours, so since he did 3½ total in 2 hours, then in 1 hour he only did half that.
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}} \\\\\\ \cfrac{7}{2}\div 2\implies \cfrac{7}{2}\div \cfrac{2}{1}\implies \cfrac{7}{2}\cdot \cfrac{1}{2}\implies \cfrac{7}{4}\implies 1\frac{3}{4}[/tex]
