Using substitution:
first you have to express one variable in terms of the other, in this we can express y in terms of x:

Since both expressions are equal to y, you have to equal both expressions like this:

Now you can solve the equation:

Knowing x=10, you can use any of the expressions we found before to find y. In this case I'm going to use y= -x+9 because it's simpler but boy should give you the same result

So, the answer is x=10 and y=-1
A = L * W
A / L = W <==
when A = 42 and W = 16.8
A / L = W
42/16.8 = W
2.5 = W <=== width = 2.5 inches
I thought doubling everytime except for the number 19000 because if you do 250 × 2 = 500 so then you do 500×2=1000.
3x=2
x= 2/3
slope is undefined. there is no y intercept
A=$20.20/10gal=$2.02 per gal
B=$26.04/12gal=$2.17 per gal
C=$28.14/14gal=$2.01 per gal
D=$30.45/15gal=$2.03 per gal
So C is the cheapest per gallon.