Applicare la formula: $a\frac{b}{c}=f$$\to ab=fc$, dove $a=y$, $b=4$, $c=3$ e $f=\frac{5}{4}x$

Applicare la formula: $\frac{a}{b}c$$=\frac{ca}{b}$, dove $a=5$, $b=4$, $c=3$, $a/b=\frac{5}{4}$ e $ca/b=3\frac{5}{4}x$

Applicare la formula: $ab$$=ab$, dove $ab=3\cdot 5$, $a=3$ e $b=5$

Applicare la formula: $ax=b$$\to \frac{ax}{a}=\frac{b}{a}$, dove $a=4$, $b=\frac{15}{4}x$ e $x=y$

Applicare la formula: $\frac{a}{a}$$=1$, dove $a=4$ e $a/a=\frac{4y}{4}$