Applicare la formula: $\frac{a}{b}c$$=\frac{ca}{b}$, dove $a=1$, $b=9$, $c=2$, $a/b=\frac{1}{9}$ e $ca/b=2\cdot \left(\frac{1}{9}\right)\cdot \left(\frac{1}{4}\right)x$

Applicare la formula: $ab$$=ab$, dove $ab=2\cdot 1$, $a=2$ e $b=1$

Applicare la formula: $\frac{a}{b}\frac{c}{f}$$=\frac{ac}{bf}$, dove $a=2$, $b=9$, $c=1$, $a/b=\frac{2}{9}$, $f=4$, $c/f=\frac{1}{4}$ e $a/bc/f=\frac{2}{9}\cdot \frac{1}{4}x$

Applicare la formula: $ab$$=ab$, dove $ab=9\cdot 4$, $a=9$ e $b=4$

Applicare la formula: $ab$$=ab$, dove $ab=2\cdot 1$, $a=2$ e $b=1$