Let's set up an equation to solve this problem. We know that the cost of a taxi ride is $5.00 plus a variable fee directly proportional to the square root of the number of miles traveled. Let C be the total cost and M be the number of miles traveled.
So, we can write the equation as:
C = $5.00 + k√M
Where k is the constant of proportionality. We can find the value of k using the information given for the 9-mile taxi ride:
$9.50 = $5.00 + k√9
Now, solve for k:
$9.50 = $5.00 + 3k
3k = $9.50 - $5.00
3k = $4.50
k = $4.50 / 3
k = $1.50
Now that we have the value of k, we can find the cost of a 36-mile ride:
C = $5.00 + $1.50√36
C = $5.00 + $1.50 * 6
C = $5.00 + $9.00
C = $14.00
So, a 36-mile taxi ride costs $14. Therefore, the correct answer is C. $14.