SOLUTION: An internet bookstore charges ₱15 shipping for orders under ₱100, but provides free shipping for orders ₱100 or more. The cost C of an order is a function of the

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That says to follow these steps for finding

C(75), C(90), C(100), C(105)

1. Look inside the parentheses following the C

2. Answer the questions about this number.  
   Is this number less than 100?
        If so, substitute this number in x+15 and simplify
        Then that will be the answer.
   Is this number greater than 100?
        If so, substitute this number into x, which means 
        that number itself is the answer.
   Is this number equal to 100?
        If so, substitute this number into x, which means 
        that number itself is the answer.

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C(75)

We look inside the parentheses following the C.
We find the number 75 inside the parentheses following the C.
We ask the question: Is 75 less than 100?
We answer yes
We substitute this number, 75, into x+15 

75+15

We simplify 75+15 and get 90
So we know that the answer is C(75) = ₱90

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C(90)

We look inside the parentheses following the C.
We find the number 90 inside the parentheses following the C.
We ask the question: Is 90 less than 100?
We answer yes
We substitute this number, 90, into x+15 

90+15

We simplify 90+15 and get 105
So we know that the answer is C(90) = ₱105

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 C(100)

We look inside the parentheses following the C.
We find the number 100 inside the parentheses following the C.
We ask the question: Is 100 less than 100?
We answer no
We ask the question: Is 100 greater than 100?
We answer no.
We ask the question: Is 100 equal to 100?
We answer yes.
We substitute this number into x, which means 
        that number 100 itself is the answer.
So we know that the answer is C(100) = ₱100

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 C(105)

We look in the parentheses following the C.
We find the number 105 inside the parentheses following the C.
We ask the question: Is 105 less than 100?
We answer no
We ask the question: Is 105 greater than 100?
We answer yes.
We substitute this number, 105, into x, which means 
        that number 105 itself is the answer.
So we know that the answer is C(105) = ₱105

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Edwin