Michael D. answered 07/01/19
Versatile STEM tutor eager to teach
Start with the 2nd given equation
-x + y = 5
Multiply both sides by 2
2*(-x + y) = 2*5
-2x + 2y = 10
As you can see "-x+2y=5" is the same as saying "-2x + 2y = 10". This is due to Multiplication Property of Equality. The Multiplication Property of Equality states that if you multiply both sides of an equation by the same number, the sides remain equal (i.e. equality is preserved).