Primitive numbers question

Hello, I was reading the article about Primitives that Guil linked in the Teacher's Notes. I have a doubt that I can't solve regarding to the second example:

// The Primitive let foo = 5;

// Defining a function that should change the Primitive value function addTwo(num) { num += 2; } // Another function trying to do the same thing function addTwo_v2(foo) { foo += 2; }

// Calling our first function while passing our Primitive as an argument addTwo(foo); // Getting the current Primitive value console.log(foo); // 5

// Trying again with our second function... addTwo_v2(foo); console.log(foo); // 5

How we can show the value "7" to the console log? I have tried adding a variable: let numberSeven = addTwo(foo) and then console logging it but I can't make it work.

Thank you.