I'll assume you mean "X" and "x" to be the same variable, as well as "Y" and "y". (This is not common usage, so, if my assumption is mistaken, I apologize.)
P = {1, 2, 4, 5, 10, 20}
Q = {-1, -2, -3, -4, -6, -12}
What is the largest product you can form (keeping in mind that, unless they say otherwise, we must assume "largest" to mean "furthest right on the number line") by multiplying a number from P by a number from Q?
Eliz.