To solve this proportion, we will use cross products
This means we multiply a by 3 and equate it by 15 times 2
[tex]\begin{gathered} a\times3=15\times2 \\ 3a=30 \end{gathered}[/tex]Now to find the value of a, we will divide both sides by 3
[tex]\begin{gathered} \frac{3a}{3}=\frac{30}{3} \\ a=10 \end{gathered}[/tex]The value of a is 10