by isabela del castillo

(houston tx )

y = 2x

x + y = 21

Replace y = 2x into the second equation.

we get:

x + 2x = 21

we get

3x = 21

divide both sides of the equation by 3

3x/3 = 21/3

x = 7

replace x in either y = 2x or x + y = 21

y = 2 times 7

y = 14