Question

Solve the real-world situation by using the substitution method.

One smartphone plan costs $30 per month for talk and messaging and $8 per gigabyte of data used each month. A second smartphone plan costs $60 per month for talk and messaging and $3 per gigabyte of data used each month. Let c represent the total cost in dollars and d represent the amount of data used in gigabytes. The system of equations lbrace c = 30 + 8d c = 60 + 3d can be used to represent this situation.

How many gigabytes would have to be used for the plans to cost the same? What would that cost be?

Both plans would cost $_____
if _____ gigabytes of data are used.

Answer 1

Plug in guesses till the answer are equal or the same. I started with 10 and 15 because I could compute that quickly and it was very close so then I saw I needed to bring one side up and one side down for the answers to be the same.
C=30+8d Data usage here would be 9= and the program would cost $102
C=60+3d. Data usage here would be14=and this program would cost $102