Final answer:
The cost of a 3-mile long cab ride would be $9, found by multiplying the distance by 3 according to the provided formula C = 3d.
Step-by-step explanation:
To calculate the cost of the cab ride using the given formula, C = 3d where C is the cost and d is the distance, you simply multiply the distance of the ride by 3. If the cab ride is 3 miles long, you will substitute 3 for d in the equation:
C = 3 × 3
By performing the multiplication, you get:
C = 9
Therefore, the cost of a 3-mile long cab ride would be $9.