Answer: 22.5+0.25x=147.50 
Explanation:
Hi, to answer this question we have to analyze the information given: 
- Flat rate: $90, (share equally among the four brothers means 90/4 =$$22.5 each) 
 - Cost per megabyte: $0.25 
 - John's share: $147.50 
 
So, the equation is 
22.5+0.25x=147.50 
Where "x" is the number of megabytes of data that john downloaded 
Feel free to ask for more if needed or if you did not understand something.