To find the single discount that is equivalent to two successive discounts of 20% and 15%, we can use the concept of net discounts.

Step 1: Find the net discount of the first discount.
The first discount is 20%. To find the net discount, we subtract the discount percentage from 100%:
Net discount = 100% - 20% = 80%

Step 2: Find the net discount of the second discount.
The second discount is 15%. Again, we subtract the discount percentage from 100%:
Net discount = 100% - 15% = 85%

Step 3: Find the single discount that is equivalent to the two successive discounts.
To find the single discount that is equivalent to the two successive discounts, we need to find the discount percentage that gives the same net discount as the two successive discounts combined.

Let's assume the single discount percentage is x%.

Using the formula for net discounts, we can set up the following equation:
(100% - x%) × (100% - x%) = 80% × 85%

Step 4: Solve the equation to find the value of x.
Expanding the equation, we get:
(100% - x%) × (100% - x%) = 80% × 85%
(100% - x%)² = 0.8 × 0.85

Taking the square root of both sides, we get:
100% - x% = √(0.8 × 0.85)

Simplifying the equation, we have:
x% = 100% - √(0.8 × 0.85)

Calculating the value, we find:
x% ≈ 100% - 0.916
x% ≈ 99.084

Therefore, the single discount that is equivalent to two successive discounts of 20% and 15% is approximately 99.084%.

Since none of the given options match the calculated value, we can conclude that the correct answer is not listed.