Math operations on numbers in JavaScript

Addition:

let a = 1 + 2;
alert(a); // shows 3

Subtraction:

let b = 3 - 2;
alert(b); // shows 1

Multiplication:

let c = 3 * 2;
alert(c); // shows 6

Division:

let d = 4 / 2;
alert(d); // shows 2

Create the variable a. Write to it the sum of the numbers 1, 2 and 3. Display the contents of the variable a, using the function alert.