Answer:
a subset of integers
Explanation:
You have to look at the definition of the variable and the meaning of the function value in order to determine suitable domain values.
Here, the variable is defined as a number of dimes. It must be a non-negative integer, a subset of the integers. (We cannot count fractional dimes or negative dimes.)
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Since the variable represents "a handful of dimes", there must be an upper limit on its value. We expect that it will be something less than 1000 (20 rolls of dimes), but it might be slightly more.