Verified answer

The greatest possible value of x is 4. For x to be the maximum number it can be, y has to be the smallest it can be. We know the smallest possible value of y is 3.

Alright well you want to substitute the lowest possible value for y which is 3

x^2+3^2≤25 -- apply the exponent

x^2+9≤25 -- subtract the 9

x^2≤16 -- sq. root both sides

x≤4

4 would be the greatest possible value for x