Answer:

Explanation:
Given
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Required
The difference in the cost of 600 text messages plan
Representing the given data as; Cost to Number of text messages, we have:

and

Multiply the dial-up by 6 to get the cost of 600


So, the cost of 600 text messages is $30 --- for dial-up
Multiply the Ring Ring by 3 to get the cost of 600


So, the cost of 600 text messages is $24 --- for Ring Ring
The difference (d) is:

