To determine how many hours Charles's fishing trip lasted based on the price he paid, we can use the equation of the line of best fit provided:
\[ y = 50x + 75 \]
where:
- \( y \) is the price of the trip,
- \( x \) is the number of hours of the trip.
Given that Charles paid $400, we need to set \( y \) to 400 and solve for \( x \):
\[ 400 = 50x + 75 \]
Step 1: Subtract 75 from both sides of the equation.
\[ 400 - 75 = 50x \]
\[ 325 = 50x \]
Step 2: Divide both sides by 50 to solve for \( x \).
\[ x = \frac{325}{50} \]
\[ x = 6.5 \]
Therefore, the number of hours of Charles's trip was 6.5 hours.