Ella and Margaret were at a carnival. They each got a ticket for the Ferris wheel. Ella got a snow cone, and Margaret got a cotton candy. Ella had a certificate for $6 off the cost. Margaret paid the rest, which came to $12.75. Each Ferris wheel ticket was $5, and a snow cone was $3.50. What was the cost for cotton candy?

The cost of Ella's ticket and snow cone was $5 + $3.50 = $<<5+3.5=8.50>>8.50.

The price Ella actually paid was $8.50 - $6.00 = $<<8.50-6=2.50>>2.50.
The cost of the cotton candy was $12.75 - $2.50 = $<<12.75-2.5=10.25>>10.25. Answer: \boxed{10.25}.

Let's break down the given information step by step:

1. We know that Ella had a certificate that subtracted $6 from the cost. So, the final cost that Ella paid for her ticket and snow cone was $12.75 - $6 = $6.75.

2. We also know that each Ferris wheel ticket cost $5, and Ella got a snow cone for $3.50. So, Ella's total cost was $5 + $3.50 = $8.50.

3. Therefore, the cost of cotton candy that Margaret paid for is the difference between the total cost Margaret paid ($12.75) and the total cost Ella paid ($8.50). So, the cost of cotton candy is $12.75 - $8.50 = $4.25.

Therefore, the cost of cotton candy was $4.25.

To find the cost of cotton candy, we need to determine the total cost and then subtract the cost of Ella's snow cone.

First, let's calculate the total cost for two Ferris wheel tickets. Each ticket costs $5, so the total cost for both tickets is $5 * 2 = $10.

Next, let's find the cost of Ella's snow cone. The snow cone costs $3.50, and Ella had a certificate for $6 off the cost. So, the final cost for Ella's snow cone is $3.50 - $6 = -$2.50.

Since Margaret paid the rest of the total cost, we can subtract Ella's snow cone cost from the total cost: $10 - (-$2.50) = $10 + $2.50 = $12.50.

Finally, we know that Margaret paid $12.75, which means the cost for cotton candy is $12.75 - $12.50 = $0.25.

Therefore, the cost for cotton candy was $0.25.