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.
In this case, Benjamin's net change in weight is a loss of 6 pounds and a gain of 8 pounds, resulting in a net gain of 2 pounds overall (8 - 6 = 2), which does not equal zero. The other situations all result in a net change of zero.