$y=-x^{2}+10 x+25$

Step 1 ：Given the equation: \(y=-x^{2}+10 x+25\)

Step 2 ：Let's assume \(x = 5\)

Step 3 ：Calculate the value of y: \(y = -5^{2} + 10(5) + 25\)

Step 4 ：\(y = -25 + 50 + 25\)

Step 5 ：\(y = 50\)

Step 6 ：\(\boxed{\text{When x = 5, y = 50 in the equation } y=-x^{2}+10 x+25}\)