Answer:
The bill will be $26070.
Step-by-step explanation:
Your base plan costs you $30 a month
And each text sent or received is only 12 cents or $0.12.
Let the messages sent be = x
So, cost for messages become = 
Let total bill cost be = y
Now, total bill will comprise of monthly plan charges plus message charges.
So, equation forms:

Now, given is that In one month 217,000 messages were sent between two brothers in Philadelphia.
So, their approximate bill will be :

=>
=> y = 26070
Therefore, bill will be $26070.