Just because there are two different units in the question doesn't mean you'll have to convert units. You never combine or mix the chocolate and the ice cream, so you can keep the units as is.

Statement (1) is sufficient. If we call the cost of each ounce of chocolate c and the cost of each pint of ice cream p, it says that 12c + 4p = 43.00. We're looking for 3c + p. If you divide the given equation by 4, the result is:
12c/4 + 4p/4 = 43/4
3c + p = 43/4

Statement (2) is not sufficient. Again, we're given an equation:
4c + 4p = 21
or:
c + p = 21/4

There's no way to find the value of 3c + p without additional information. Choice (A) is correct.