Declaring variables in programming is a fundamental concept that allows you to store and manipulate data. Variables are used to store values that can be accessed and modified throughout the program.

In Rust, variables are declared using the let keyword followed by the variable name and an optional type annotation.

In Rust, variables are immutable by default. This means that once a value is bound to a variable, it cannot be changed. This is a key feature of Rust that helps ensure safety and prevent bugs by avoiding unexpected changes to values.

In this challenge, you will declare and use immutable variables in Rust. You will be given a function where you need to declare variables and use them to perform specific operations. The goal is to get comfortable with the concept of immutability and understand how to use immutable variables effectively.

Your task is to define two immutable variables inside the function using the let keyword:

• width with a value of 10
• height with a value of 5

Then, calculate the area of a rectangle using the formula area = width * height and return the calculated area.

• Declare two immutable variables, width and height, and assign them values.
• Calculate the area of the rectangle using the formula width * height.
• Return the calculated area.

• Use the let keyword to declare variables.
• Remember that variables declared with let are immutable by default.
• Use multiplication * to calculate the area.