Lin earns $12 an hour. she wants to buy a new mp3 player. she is considering going models that cost at least $84.

It was a little unclear on what the question was overall asking for...
But here's what I came up with,
Since Lin earns $12 per hour, it will take her a total of 7 hours for her to have $84 so she can purchase her MP3 player.
Explanation:
84 divided by 12 = 7 hours
Final It will take Lin a total of 7 hours to have the enough to purchase her MP3 player.
Hope this was found helpful for you!
It was my pleasure assisting you.

Equation: 

When adding or subtracting, you have to make sure they have a common denominator

So you have to multiply  by 



Since they both have the same denominator, you subtract



One thing to note is when subtracting, you DO NOT subtract the denominator, only the numerators

To reduce to the lowest terms, you need to find a common factor.
5 goes into 10 two times and goes into 15 three times

 ÷ 

 ÷ 

That leaves it with the fraction