MY Very LAST math problem! Can Anyone Assist? Assistance Please

The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 33 minutes of calls is $24.72 , and the remaining credit after 62 minutes of calls is $20.08 . What is the remaining credit after 70 minutes of calls?

Thanks

(24.72 - 20.08) / (33 - 62) =
4.64 / -29 =
-0.16

The cost for each minute of calls is 16 cents, so the value on the card drops by 16 cents for each minute that is used.

20.08 - (70 - 62) * 0.16 =
20.08 - 8 * 0.16 =
20.08 - 1.28 =
18.80

So after 70 minutes of calls, the card should have $18.80 credit remaining.

Note that in this case, I used the second set of numbers in the final calculation ($20.08 after 62 minutes, minus the cost of the additional 8 minutes between 62 minutes and 70 minutes used.) But because the equation is linear, we could use either set of numbers to start. After 33 minutes, we have $24.72 credit remaining, so:

24.72 - (70 - 33) * 0.16 =
24.72 - 37 * 0.16 =
24.72 - 5.92 =
18.80

See? The answer is the same either way.

This is the exact same as your other questions, now the gradient is negative.

Work it out the same way we've worked it out over and over again now.

Find the rise over run of the two points you're given (33, 24.72) and (62, 20.08) and that gives you the gradient. Plug the gradient into either of the equations given by one of your points to find the y intercept.

You'll get a positive intercept (the amount of credit you start with), and a negative gradient. Put in 70 minutes into the equation of the line and find the remaining credit.

Each month starts a new amount of credit in dollars. This would be the same amount each month, but unknown. We'll call that "c".

We know that each minute costs something, but we just don't know how much yet. We'll call that "m".