Mary purchased a prepaid phone card for $30.00. Calls cost 20 cents a minute using this card. The credit, C (in dollars), left on the card after it is used for x
minutes of calls is given by the following.
C = 30.00 -0.20x
How much credit is left on the card after Mary uses it for 50 minutes of calls?

$40 is left on the card after Mary uses it for 50 minutes of calls.

Step-by-step explanation:

Let x represent the number of minutes of calls made

The credit, C (in dollars), left on the card after it is used for x

minutes of calls is given by the expression,

C = 30.00 -0.20x

After Mary used the credit for 50 minutes of calls, the amount of credit that would be left on the card is

C = 30.00 - 0.20 × 50

C = 30 + 10

C = $40

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