Jack has y chocolates and Jill has x chocolates.
If Jack gives 1 chocolate to Jill, then they will have an equal number of chocolates.
If Jill gives 1 chocolate to Jack, then Jack will have twice as many chocolates as Jill.
How many chocolates does Jill have?
Jack has 2 more chocolates than Jill.
They can't have very many; so, start low:
If Jack has 3 and Jill has 1, then, when Jill has given one chocolate to Jack, Jack will have 4 and she won't have any, so Jack's number won't be twice as many as Jill.
Try 4 and 2, then 5 and 3, then 6 and 4, then 7 and 5 --
At 7 and 5, if Jack gives one to Jill, they both will have 6 and if Jill gives 1 to Jack, he'll have 8 and she'll have 4 (and Jack will have twice as many as Jill).
Jill has 5.