Answer
The number of GB is $ 2 $
Work Step by Step
Let $ x $ represents number Of GB of data used.
for Data plan A.
Monthly fee is $ = \$ 40 + 15 \times $ number of GB used.
In mathematical form.
Monthly fee $ = \$ 40 + 15 \times x $.
For data plan B.
Monthly fee is $ = \$ 30 + 20 \times $ number of GB used.
In mathematical form.
Monthly fee $ = \$ 30 + 20 \times x $.
To find the costs for the two data plans be the same, equate both monthly fees.
$ 40 + 15 \times x = 30 + 20 \times x $
$ 40 -30 = 20 \times x - 15 \times x $
$ 10 = 5x $
$ \frac{10}{5} =x $
$ 2=x $.
