Question

Jordan wants to solve the following system using the elimination method:

2x + 3y = 10
x + y = 7

What number should the equation x + y = 7 be multiplied by to eliminate y?

−2
2
−3
3

Answer 1

You have to multiply by -3 because you'll have :
2x+3y = 10
x+y = 7  | *(-3)

2x+3y = 10
-3x - 3y = -21 
_____________+
-x = -11 (so you eliminated y)

Answer 2

3 should be your answer

In elimination, you are already subtracting the whole of one equation

2x + 3y = 10 - 3(x + y = 7)

Distribute 2 to all monomials in the equation inside the parenthesis:
3x - 3y  = 21

Combine:
  2x + 3y = 10
+3x - 3y  = 21
-------------------
   5x         = 31


hope this helps