Question 104253
Let's find an equation for each car rental. 
{{{A = 28*D}}}
{{{T = 108*W+0.14*M}}}
Since there is a difference between the days equation and the weeks equation. Let's change the first one to be on a week basis also. Since there are 7 days in a week, we multiply by 7.
{{{A=7*28*W}}}
{{{A=196W}}}
Let's find out when Avis and Toyota would be the same price.
{{{A=T}}}
{{{196W=108W+0.14*M}}}
{{{196W-108W=0.14*M}}}
{{{88W/0.14=M}}}
{{{629W=M}}}
So if you drive 629 miles in one week. Avis and Toyota will have the same price for the rental. If you drive more than 629 miles in a week, Toyota will have the higher price. In other words, your mileage rate where you start to pay more is 629 miles/week. This gets you around not knowing how many days you have the rental. 
Check your answer. 
Let's say you drove 1500 miles in two weeks.
Since 1500 miles > 2 weeks*629 miles/week (1258 miles), you would expect Toyota to be higher in cost.  
Avis would charge you :
{{{A=28*14=392}}}
Avis' charge is $392. 
Toyota would charge you :
{{{T=108*2+0.14*1500=206}}}
Toyota's charge is $426. 
Toyota is $34 more than Avis, as you expected.