I’m pretty sure the answer is m= -6/5 I’m not sure tho
Since you have y alone on one side of the equation......
Use substitution and plug in 1/2x-4 for y in the other equation.

Distribute

Combine like terms

Add 8 to both sides

Divide by 4
and 
Plug this value in for x

Simplify

Multiply everything by 8 and simplify

Divide.....

Your answers are:

Answer:
The width (in our case it is the height) of the rectangle equals 17 miles
Step-by-step explanation:
In order to solve this, we need to know the following...
Area of a rectangle = Length x Width
(in our case based on what you said length is the base and width is the height)
Now we just change the formula to our needs and get that...
Width = Area of the rectangle / Length
And so we get...
Width = Area of the rectangle / Length
Width = 226.1 / 13.3
Width = 17 miles
12x - 4y = -8
y = 3x + 2
Rewrite the first equation
12x + 8 = 4y
3x + 2 = y
As you see, the first and second equation are actually the same, meaning there's an infinite number of solutions.