Answer:

Step-by-step explanation:
A ratio is a comparison of two quantities and can be written in several forms including fractions. It is most commonly written in fraction form or a:b.
To write a ratio, we count the number of each quantity we are comparing or use the variable for that quantity. We write radius:circumference. Recall, the circumference of a circle can be found using
or
.
We write r:
or r:
.
We can also write in fraction form:
or 
It's equal to -15 because you are dividing by an negative and if it's only 1 negative number in your equation then your answer will be a negative and if it's 2 negatives then it would be a positive answer
Answers:
10) y= 1/2x - 2
11) y= 2x + 3
12) y= 2/3x - 4
I found this by using y=mx+ b