Question

X = -2y + 300 3y = 800 - 4x

Answer 1

x=140, y=80.

Explanation:

x=-2y+300

3y=800-4x

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3y=800-4(-2y+300)

3y=800+8y-1200

3y-8y=800-1200

-5y=-400

5y=400

y=400/5

y=80

x=-2(80)+300

x=-160+300

x=140

Answer 2

x = 140, y = 80

Explanation:

`\left\{\begin{array}{ccc}x=-2y+300&(1)\\3y=800-4x&(2)\end{array}\right\\\\\text{Substitute (1) to (2):}\\\\3y=800-4(-2y+300)\qquad\text{use the distributive property:}\ a(b+c)=ab+ac\\\\3y=800+(-4)(-2y)+(-4)(300)\\\\3y=800+8y-1200\\\\3y=8y-400\qquad\text{subtract}\ 8y\ \text{from both sides}\\\\-5y=-400\qquad\text{divide both sides by (-5)}\\\\y=80\\\\\text{Put it to (1):}\\\\x=-2(80)+300\\\\x=-160+300\\\\x=140`