Can anyone explain me.

Question

function x(a=1,b=5,c=6){
return a+b-c;
}
document.write(x(7,4)); //5

Answer 1

When you declared function you set agruments by default parameters (a=1, b=5, c=6), so when you used function you gave new parameters to "a=7" and "b=4", thus comp gets your code like this:
document.write(x(7,4)); //return 7+4-6

Answer 2

Thank u so much Umid