Question 1199969
<font color=black size=3>
x = number of miles driven
y = total cost in dollars


Plan A: 
y = 0.18x+30


Plan B:
y = 50


The variable x is not involved with the cost equation of plan B, since there's unlimited mileage. 
You drive as much as you want and pay the same flat rate of $50.


Use substitution to solve for x.
y = 50
0.18x+30 = 50
0.18x = 50-30
0.18x = 20
x = 20/(0.18)
x = 111.111111111111
That value is approximate.


If you drove 111 miles, then plan A costs 
y = 0.18*x+30
y = 0.18*111+30
y = 49.98
Meaning that plan A is the cheaper option for this mileage.


But if you drove 112 miles, then plan A costs
y = 0.18*x+30
y = 0.18*112+30
y = 50.16
Showing that plan B is now the better choice.


To save money with plan B, the mileage must be <font color=red>greater than <u>&nbsp;&nbsp;111&nbsp;&nbsp;</u> miles per day</font>
In other words, the mileage must be 112,113,114,etc if the mileage is an integer.
</font>