Step-by-step explanation:
4x+9y=28
-4x-y=-28
8y=0
divide both side by 8
y=0
solve for X in equation 1
4(X)-9(0)=28
4x-0=28
4x =28
divide both side by 4
4x/4=28/4
X= 7
y=0,x=7
Answer: 15
<u>Step-by-step explanation:</u>
small: 5 12 13
middle: __ 36 39
large: 45 108 117
Notice that to get from the small to the large, multiplied by 9
5(9) = 45 12(9) = 108 13(9) = 117
That is because the sides are proportional
To get from small to middle, multiply by 3
5(3) = 15 12(3) = 36 13(3) = 39
To solve it using proportions:

Method 1:
Convert the mixed number to the improper fraction:

Make the product:

<em>canceled 2</em>

Method 2:


<em>use the distributive property a(b + c) = ab + ac</em>

His mistake was adding 12+2 when he was supposed to subtract.