Final answer:
The expression c + 0.15c can be simplified to 1.15c.
Step-by-step explanation:
The expression c + 0.15c represents the cost of Noah's lunch after a 15% tip. To simplify this expression, we can factor out the common term, c, from both terms. This gives us c(1 + 0.15), which simplifies to 1.15c.
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