Can someone tell me how this is wrong

Answer:
y = 17
Step-by-step explanation:
We have five values : 2 , 5 , 7 , y , 9
and the mean = 8
this means :
[tex]\frac{2+5+7+y+9}{5} =8\\\\then\\\\23+y = 8*5\\\\then\\\\y = 40 - 23\\\\then\\\\y=17[/tex]
Verification: (2+5+7+17+9)÷5 = 8