Let N be the number of subs, then we can write the following relationship:
[tex]5.10\cdot N=19.5[/tex]That is, this equality gives us the number of subs we can buy. If we move 5.10 to the right hand side, we have
[tex]\begin{gathered} N=\frac{19.50}{5.10} \\ N=3.82 \end{gathered}[/tex]this means that we can buy 4 subs approximately.
