Mr. Johnson is also comparing the two mobile phone data plans. Talk First charges $20 plus $5 per GB of data, while Mobile Plus charges $30 plus $3 per GB of data. At what amount of GB use will the cost of the two data plans be the same? Mr. Johnson wrote this equation for the scenario. 1. d = amount of data used (GB)

2. Talk First = Mobile Plus

3. 20d + 5 = 30d + 3

Analyze Mr. Johnson’s work and identify his mistake.
A In step 1, his variable should be c, representing company.
B In step 2, his translated equation should be Talk First + Mobile Plus = Total
Money.
C In step 3, he multiplied the variable by the base monthly cost instead of by the
cost per GB.