(b)
Casework for topping version of 3 - 3, 3 - 4, 3 - 5, 4 - 4, 4 - 5, and 5 - 5
3 - 3: 10 choose 3 * 7 choose 3 = 4200
3 - 4: 10 choose 3 * 7 choose 4 = 4200
3 - 5: 10 choose 3 * 7 choose 5 = 2520
4 - 4: 10 choose 4 * 6 choose 4 = 3150
4 - 5: 10 choose 4 * 6 choose 5 = 1260
5 - 5: 10 choose 5 * 5 choose 5 = 252
Add them all together: 15582