[tex]\underbrace{3\times1}_{first}-\frac{3}{4}=3-\frac{3}{4}=2\frac{1}{4}[/tex]
[tex]3\times1\frac{3}{4}=3\times\frac{1\times4+3}{4}=3\times\frac{4+3}{4}=\frac{3}{1}\times\frac{7}{4}=\frac{3\times7}{4}=\frac{21}{4}=\frac{20+1}{4}=\frac{20}{4}+\frac{1}{4}\\\center\boxed{=5\frac{1}{4}}[/tex]
