book: ch03-01(shadowing): Clarify RHS evaluation order

src/ch03-01-variables-and-mutability.md

@@ -140,12 +140,15 @@ use of the `let` keyword as follows:
 ```
 
 This program first binds `x` to a value of `5`. Then, it creates a new variable
-`x` by repeating `let x =`, taking the original value and adding `1` so that
-the value of `x` is `6`. Then, within an inner scope created with the curly
-brackets, the third `let` statement also shadows `x` and creates a new
-variable, multiplying the previous value by `2` to give `x` a value of `12`.
-When that scope is over, the inner shadowing ends and `x` returns to being `6`.
-When we run this program, it will output the following:
+that is also called `x`, by repeating `let x =`. The program takes the original
+value of `x` and adds `1`, so that the value of the new variable `x` is now `6`.
+It is important to understand that the right-hand side is evaluated first `(5 + 1)`
+before this value is assigned to the new variable `x`. Then, within an inner
+scope created with the curly brackets, the third let statement also shadows `x`
+and creates a new variable, evaluating the right-hand side first `(6 * 2)`
+before assigning `12` to the new `x`. When that scope is over, the inner
+shadowing ends and `x` returns to being `6`. When we run this program, it will
+output the following:
 
 ```console
 {{#include ../listings/ch03-common-programming-concepts/no-listing-03-shadowing/output.txt}}