SOLUTION: I don't understand this method of solving? could you show me both parts of this problem in the long form for my reference. Solving: 4x+9y = 395 1x+y = 80 Us

Question 166627: I don't understand this method of solving? could you show me both parts of this problem in the long form for my reference.
Solving:
4x+9y = 395
1x+y = 80

Using Substitution Method.
Expressing x as a function of y (from the first equation) x = (395 -9y)/4
Substituting this expression into the second equation:
1(395+9y)/4+y = 80
Simplifying this expression:
(-5)y = -75

Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Note: I'm going to make the first equation and the second equation (it is valid to relabel the equations)

Start with the given system of equations:

Now in order to solve this system by using substitution, we need to solve (or isolate) one variable. I'm going to solve for y.

So let's isolate y in the first equation

Start with the first equation

Subtract from both sides

Rearrange the equation

---------------------

Since , we can now replace each in the second equation with to solve for

Plug in into the second equation. In other words, replace each with . Notice we've eliminated the variables. So we now have a simple equation with one unknown.

Distribute to

Multiply

Combine like terms on the left side

Subtract 720 from both sides

Combine like terms on the right side

Divide both sides by -5 to isolate x

Divide

-----------------First Answer------------------------------

So the first part of our answer is:

Since we know that we can plug it into the equation (remember we previously solved for in the first equation).

Start with the equation where was previously isolated.

Plug in

Multiply

Combine like terms

-----------------Second Answer------------------------------

So the second part of our answer is:

-----------------Summary------------------------------

So our answers are:

and

which form the ordered pair

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