Exercise 1: Rectangle Struct with a mutating scale(by:) Method — Possible Solution
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struct Rectangle {
    var width: Double
    var height: Double

    mutating func scale(by factor: Double) {
        width *= factor
        height *= factor
    }
}

var original = Rectangle(width: 10, height: 5)
var copy = original
copy.scale(by: 2)

print(original.width)   // Prints: 10.0
print(copy.width)       // Prints: 20.0

HOW IT WORKS: Rectangle is a struct, so `var copy = original` creates
a genuinely independent copy of original's own current values, not a
shared reference to the same instance. Calling copy.scale(by: 2)
mutates only that copy - doubling copy's own width and height in
place - and has no effect whatsoever on original, since the two
variables now hold entirely separate values with no connection between
them.

The mutating keyword on scale(by:) is required because the method
reassigns width and height, which a struct's own regular (non-mutating)
methods aren't allowed to do - and calling it requires copy to be a
var, since a let-declared struct could never accept a mutating call.

ANSWER: original.width stays 10.0 and copy.width becomes 20.0 after
scaling only the copy, confirming that assigning a struct to a new
variable creates a genuinely independent copy - mutating one has no
effect on the other, since they no longer share any underlying state
once the copy was made.

WHY THIS WORKS AS AN ANSWER
------------------------------
This correctly implements a mutating struct method and demonstrates,
with printed real values, that copying a struct and mutating the copy
leaves the original completely untouched - the defining behavior of a
value type.