We are given
A cell phone company charges $45 a month for phone service and
$0.25 for each text message
(a)
Let's assume
total number of messages sent on each month is x
total monthly bill is $ y
so, we can set up equation
[tex]y=45+0.25x[/tex]
now, we can solve for x
Subtract both sides by 45
[tex]y-45=45+0.25x-45[/tex]
[tex]y-45=0.25x[/tex]
[tex]x=\frac{y-45}{0.25}[/tex]
[tex]x=4y-180[/tex]...........Answer
(b)
we can plug y=75
and then we can solve for x
[tex]x=4*75-180[/tex]
[tex]x=300-180[/tex]
[tex]x=120[/tex]
so, total number messages sent were 120...........Answer
