Applicare la formula: $\frac{a}{b}\frac{c}{f}$$=\frac{ac}{bf}$, dove $a=3$, $b=4$, $c=y$, $a/b=\frac{3}{4}$, $f=3$, $c/f=\frac{y}{3}$ e $a/bc/f=\frac{3}{4}x\frac{y}{3}$

Applicare la formula: $ab$$=ab$, dove $ab=4\cdot 3$, $a=4$ e $b=3$

Applicare la formula: $\frac{ab}{c}$$=\frac{a}{c}b$, dove $ab=3y$, $a=3$, $b=y$, $c=12$ e $ab/c=\frac{3y}{12}$

Applicare la formula: $\frac{ab}{c}$$=\frac{a}{c}b$, dove $ab=3y$, $a=3$, $b=y$, $c=12$ e $ab/c=\frac{3y}{12}$