To represent the situation with an equation, we start by noting that a regular pentagon has 5 equal sides. If each side is represented by \( x + 6 \), then the total perimeter \( P \) of the pentagon can be expressed as:
\[ P = 5 \times \text{(length of one side)} = 5(x + 6) \]
According to the problem, the perimeter of the pentagon is 84. Therefore, we can set up the following equation:
\[ 5(x + 6) = 84 \]
This equation represents the situation provided.