Solution:
According to the information given in the problem, we get the following equation:
[tex]\frac{ER}{30}=\frac{13}{65}[/tex]
By cross-multiplication, we get:
[tex](ER)(65)=(13)(30)[/tex]
this is equivalent to:
[tex](ER)(65)=390[/tex]
solving for ER, we get:
[tex]ER\text{ =}\frac{390}{65}=6[/tex]
so that, we can conclude that the correct answer is:
[tex]6[/tex]
