Final answer:
The expression c+0.15c can be simplified to c(1.15).
Step-by-step explanation:
The expression c+0.15c represents the cost of Noah's lunch after a 15% tip. To simplify the expression, we can factor out the common factor of c from both terms:
c+0.15c = c(1 + 0.15) = c(1.15)
So, the simplest form of the expression is c(1.15).