Exercise 1: Chaining Coffee, Whip, Milk, Sugar — Possible Solution
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BUILDING THE CHAIN IN THE STATED WRAPPING ORDER
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"Coffee, Whip, Milk, Sugar" means the base SimpleCoffee is wrapped
first by WhipDecorator, then that result is wrapped by MilkDecorator,
then that result is wrapped by SugarDecorator (the outermost layer):

    base  = SimpleCoffee()
    step1 = WhipDecorator(base)
    step2 = MilkDecorator(step1)
    step3 = SugarDecorator(step2)

HAND CALCULATION
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Each decorator's cost() call adds its own amount on top of whatever
the wrapped object underneath already reports:

    base cost                 = 2.00
    + WhipDecorator  (0.75)   = 2.75
    + MilkDecorator  (0.50)   = 3.25
    + SugarDecorator (0.30)   = 3.55

VERIFYING AGAINST THE ACTUAL CODE
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Running step3.description() and step3.cost() gives:

    description: 'Coffee, Whip, Milk, Sugar'
    cost: 3.55

Both match the hand calculation exactly - the description builds up
in the same order the objects were wrapped in, and the cost is the
sum 2.00 + 0.75 + 0.50 + 0.30 = 3.55.

WHY THIS WORKS AS AN ANSWER
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The wrapping order is followed literally as stated in the exercise
(each named decorator wraps the previous result, left to right), the
hand calculation is shown step by step rather than jumping to the
total, and the result is confirmed against the actual running code
rather than only asserted.