The situation that is NOT an example of two quantities that combine to make zero is:
Benjamin lost 6 pounds and then gained 8 pounds.
This situation does not result in a net zero, as losing weight and then gaining a different amount does not cancel out to zero. In fact, it results in a net loss of 2 pounds.
The other situations (Mary with bottle caps, a business's income and expenses, and Madeline's win and payment to the babysitter) all result in a net cancellation to zero.