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