You must use substitution method
x+y=7
2x+y=10

x = 3, y = 4

Step-by-step explanation:

First, set the first equation equal to x. Note the equal sign, what you do to one side, you do to the other.

Subtract y from both sides of the equation:

x + y = 7

x + y (-y) = 7 (-y)

x = 7 - y

Next, plug in 7 - y for x in the second equation:

2x + y = 10

2(7 - y) + y = 10

Simplify. First, distribute 2 to all terms within the parenthesis:

2(7 - y) = (2 * 7) + (2 * -y) = 14 - 2y

Next, combine like terms. Like terms are terms with the same amount of the same variables:

14 - 2y + y = 10

14 (-2y + y) = 10

14 - y = 10

Isolate the variable, y. First, subtract 14 from both sides of the equation:

-y + 14 (-14) = 10 (-14)

-y = 10 - 14

-y = -4

Next, isolate the variable, y, by dividing -1 from both sides of the equation:

(-y)/-1 = (-4)/-1

y = -4/-1 = 4

Next, plug in 4 for y in one fo the given equations:

x + y = 7

x + (4) = 7

Isolate the variable, x. Subtract 4 from both sides of the equation:

x + 4 (-4) = 7 (-4)

x = 7 - 4

x = 3

x = 3, y = 4