Question

Which equation will result if the substitution method is used to solve the following system of linear equations?

x – y = 7
x = y + 3

A.
(y + 3) – y = 7

B.
x – y = y + 3

C.
x = (7 – x) + 3

D.
x – (y + 3) = 7

Answer 1

If you help me quickly, I will fan and medal. This is my last question! :)

Answer 2

It is nice that one of those equations has a variable alone on one side. The second equation can be used to substitute the X in the first equation with (y+3). Just make that substitution and you will have your answer.

Answer 3

I am terrible at this. I don't understand...:/

Answer 4

That's okay, we just have to go about it a different way :)

Okay, so you have:
x - y = 7
x = y + 3

Now, see that in Equation 2, it states that X = y + 3. Well, now that you know that X = (y + 3), you can plug (y + 3) into anywhere that X appears in the other equation! :D

Soooo, look at Equation 1 again. See any X's? Now just replace (or "substitute") that X with your (Y + 3) :)

Let me know if you're still confused so I can help!

Answer 5

Well notice

x – y = 7
x = y + 3

That second equation there...tells us what 'x' equals.....x equals (y + 3)

since we know that...we can use it in the first equation....now our first equation was

x - y = 7

But since we know that x = y + 3 we can now replace every 'x' we see ..with what 'x' equals...so for every 'x' you see...replace it with the y + 3

(y + 3) - y = 7