From the question, we are informed that in June, Clarissa used 1 gigabytes of data on her cell phone. Since June has 30 days, the amount of data she uses on average per day? will be:
so i basically took 12 and added that to 18 [and got 30] to find out how many degrees it went up and then i solved each equation till i got 30. I hope this helped and that you could understand the way i did it.