Question 1189195
.
Marisol has two different methods of commuting to and from work: 
she either takes the subway, which costs $2.75 per one-way trip, or she takes a car service, which costs $18.50 per one-way trip. 
Last week, she worked 5 days, commuting to and from work each day. If her total commuting cost for the week was $74.75, 
how many times did she take the car service?
~~~~~~~~~~~~~~


<pre>
Let  x  be  "how many times did she take the car service" (the unknown value under the problem's question).


Then for the subway trips, we have the number 5*2 - x = 10-x.


After that, we write the "money equation"


    2.75*(10-x) + 18.50x = 74.75  dollars.


From the equation,


    x = {{{(74.75 - 2.75*10)/(18.50-2.75)}}} = 3.


<U>ANSWER</U>.  She took car service 3 times, and she used the subway 10-3 = 7 times.


<U>CHECK</U>.  3*18.50 + 7*2.75 = 74.75 dollars, in total.   ! Correct !
</pre>

Solved, checked and explained.