In the equation \( y = 12x + 20 \), \( y \) represents the total cost to rent the boat, \( x \) represents the number of hours rented, and the equation indicates that there is a base fee of $20 plus $12 for each hour.
To find the cost to rent a boat for 8 hours, substitute \( x = 8 \) into the equation:
\[ y = 12(8) + 20 \]
Calculating this gives:
\[ y = 96 + 20 = 116 \]
Therefore, the cost to rent the boat for 8 hours is $116.