Answer: -3x + 4, (2,-2)
Step-by-step explanation:
First, you want to get y alone on one side.
3x + y = 4
-4 -4 subtract 4 to get it on the left side.
-y -y subtract y to get it alone on the right side.
Your'e left with 3x - 4 = -y divide the whole equation by -1 do get a pos y
You then have y = -3x + 4. That's the first part of your answer.
To get the second part plug in (-3x + 4) into the y of the first equation, this is the substitution part.
-2x + 5(-3x+4) =-14 distribute the 5... -2x - 15x +20 = -14
add your like terms ( x and x) -17x + 20 = -14
Isolate your x by subtracting the 20, both sides -20 -20
-17x = -34 divide both side by 17 you get x = 2 (---- this is your first coordinate in the pair in your answer. To get the y do the same but solve for y instead of x.
. Profit function is 
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. In a day, bookstore must sell at least 15 books, because of 6n-90=0, in order to make profit.
