30 M&Ms
1) Gathering the data
12-ounce bag of trail mix = 18 M&Ms
20-ounce bag=?
2) Assuming that the M&Ms are placed in following a constant rate we can write the following proportion:
12 --------------- 18
20 --------------- y
<em>Cross multiplying it due to the first property of proportions</em>
<em />
12y =20 x 18
12y = 360
y=30
3) So, I'd expect to find 30 M&Ms at a 20-ounce bag of trail mix.
In customary units, the length of a car would be in feet.
Answer:
The system has zero solutions.
You want to isolate the variable 'y'.

Subtract 10 to both sides:

Divide -3 to both sides: