The scope inside a nested function

Look at this example of nested function:

function outer() {
  var a = 4, b = 8;

  function inner() {
    var b = 10, c = 15;
    return a+b+c; 
  }

  b = 6;

  return inner();
}

What is the value of 'v' returned by function outer below?

var v = outer(); // ??