SOLUTION: I am studying for my 8th grade algebra final and i dont understand the way that on this linear system 4x+5y = 7 6x-2y = -18 how do i do this

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Question 2754: I am studying for my 8th grade algebra final and i dont understand the way that on this linear system 4x+5y = 7
6x-2y = -18
how do i do this x = (7 -5y)/4
Substituting this expression into the second equation:
6(7+5y)/4-2y = -18


and from after that how do i simplify this 6(7+5y)/4-2y = -18
into this (-38)y = -114
I listen in class but i was absent on some very important days and this doesnt make sence
I thank anyone who could help.

GOD BLESS YOU ALL
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
this x+=+%287+-5y%29%2F4 is correct, well done.

this 6%287%2B5y%29%2F4-2y+=+-18 is not correct as you have +5y..it should be -5y. I guess this was just a simple typo error?.

anyway, correct version is: 6%287-5y%29%2F4-2y+=+-18

First multiply every term by 4:
4%2A6%287-5y%29%2F4+-+8y+=+-72 so that the fraction in the first term cancels itself:

6%287-5y%29+-+8y+=+-72
42+-+30y+-+8y+=+-72
42+-+38y+=+-72
-38y+=+-114
y = 3

Now sub this back into eiter equation - pick the one that looks the easiest! I pick the first equation:

4x+5y = 7 becomes 4x+%2B+5%2A3+=+7...

4x+%2B+15+=+7
4x+=+-8
x+=+-2

DEFINITELY put these answers in the second equation, to make sure that they equal to -18...

6x-2y becomes 6%28-2%29+-+2%283%29

-12+-+6
-18

so the answer is DEFINITELY correct.

jon