To find the cost of each of the first three tires, we can set up the equation based on the given information. Let the cost of each of the first three tires be \( x \).
According to the deal, if he buys three tires and gets the fourth for $5, the total cost of all the tires can be expressed as:
\[ 3x + 5 = 237.50 \]
To isolate \( 3x \), subtract 5 from both sides:
\[ 3x = 237.50 - 5 \] \[ 3x = 232.50 \]
Next, divide both sides by 3 to solve for \( x \):
\[ x = \frac{232.50}{3} = 77.50 \]
Therefore, the cost of each of the first three tires is \( \mathbf{77.50} \). So, the correct answer is:
$77.50