Explanation

The question tells us that the people are lined up such that their ages are 15, 17, 19, 21, 23, and so on, up to an upper limit that is not told to us. If we get the information we need to write out all of the exact ages, then the sum is calculable (though we won't bother to calculate it, of course). On to the data statements. Statement (1) would allow us to determine the complete sequence; we can tell that without writing out all 37 terms, because we know we could. So it's sufficient. Statement (2) is also sufficient, because it gives us the last term and hence would allow us to write out the entire sequence. By the way, in either case, the sum itself is not too difficult to calculate, because we can manipulate the formula for the average of numbers to do so. But we don't have to do that here.

The correct answer is (D).