Let the cost of each of the first three tires be \( x \). According to the deal, the cost of the fourth tire is $5.
The total cost for the four tires can be expressed as:
\[ 3x + 5 = 237.50 \]
Subtracting 5 from both sides gives:
\[ 3x = 237.50 - 5 \]
\[ 3x = 232.50 \]
Now, divide both sides by 3 to find \( x \):
\[ x = \frac{232.50}{3} = 77.50 \]
Thus, the cost of each of the first three tires is $77.50.