Why I const “y” it give me a error :ReferenceError: Cannot access ‘y’ before initialization

I try to fix this but it say error many time and it give me a error :ReferenceError: Cannot access ‘y’ before initialization
I also change the const to var or let and change the position in the code but it not change
Plz who can fix me this code:

let x = toCelius(8,10);

function toCelius(c,f){

return (100+1) * (c+f);

}

document.getElementById(“demo”).innerHTML=x;

const y=to(9);

function to(){

return (y+10)

}

document.getElementById(“p1”).innerHTML=y;`