Please explain me why value of "y" doesn't change after the "foo" function?

Question

https://code.sololearn.com/W30SlRFoiIRn/?ref=app

Answer 1

y = 7;
function foo() {
y = 4;
}
foo();
alert(y);

Answer 2

because you only change the value of x,

there is only one statement that changes a variable it's x=4;

Answer 3

Ok, but how to change the value of y?

Answer 4

Thank you very much