Answer:
1. y=0.35x+35
2. If 979 minutes are used, the total cost will be $377.65 dollars.
Step-by-step explanation:
1. Let $x be the flat monthly fee and $y be the amount of money paid per minute used on the phone.
If a customer uses 210 minutes, the monthly cost will be $108.5, thus
[tex]x+210y=108.5[/tex]
If the customer uses 620 minutes, the monthly cost will be $252, then
[tex]x+620y=252[/tex]
Subtract from the second equation the first one:
[tex]x+620y-(x+210y)=252-108.5\\ \\x+620y-x-210y=143.5\\ \\410y=143.5\\ \\y=0.35[/tex]
Substitute it into the first equation
[tex]x+210\cdot 0.35=108.5\\ \\x=108.5-73.5\\ \\x=35[/tex]
We get the flat fee is $35 and the amount of money per minure used is $0.35. So, the equation of the function is
[tex]y=35+0.35x,[/tex]
where x is the number of monthly minutes used and y is the total monthly of the NextFell plan.
2. When x=979, then
[tex]y=35+0.35\cdot 979=377.65[/tex]
