first off, we need to convert the mixed fraction to "improper", and then just multiply linearly, let's do so,
[tex]\bf \stackrel{mixed}{3\frac{4}{7}}\implies \cfrac{3\cdot 7+4}{7}\implies \stackrel{improper}{\cfrac{25}{7}}
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\cfrac{1}{2}\cdot \cfrac{25}{7}\implies \cfrac{1\cdot 25}{2\cdot 7}\implies \cfrac{25}{14}\implies 1\frac{11}{14}[/tex]