Question 2157c59a

Each side of a $30$-sided polygon has one of three lengths. The number of sides with length $8 \text{centimeters} \left(\text{cm}\right)$ is $5$ times the number of sides $n$ with length $3 \text{cm}$. There are $6$ sides with length $4 \text{cm}$. Which equation must be true for the value of $n$?