9 plus 7 equals 16.
60.
22
One solution.
The answer is (3.5)2 plus (4)2 equals 410.
7.5
Not sure what you mean; that equation certainly has a solution.
(x, y) = (3, 7) is a solution.
73
Another solution for x+y = 7 is y = -x+7
The solution is (x, y, z) = (2.5, 1, 2.5).
x = -3, y = 7