The first question is different from the second question, that is to say, the maximum value of xy is x+y, so naturally your second question takes X = 8 and Y = 8.

Positive solution;

If you divide xy by the same number, you know that 2/y+8/x= 1, and then multiply it by x+y to get x+y =10+2x/y+8y/x.

The rest, you know.

Don't forget to test whether the mean inequality exists when taking the equal sign.