Answer :
The charge is $75 per month plus a one-time activation fee of $50.
We can model the total cost as:
[tex]f(m)=75\cdot m+50[/tex]where m is the number of months.
If he uses for 10 months (m=10), the total cost is:
[tex]f(10)=75\cdot10+50=750+50=800[/tex]The total cost for 10 months is $800.