Answer:
20
Explanation:
start by using system of equations
x = cola
y = root beer
x + y = 30
x = 2y
now either use substitution or elimination. for me, substitution is easier.
the second equation already has one variable isolated ( x ) so, plug that into the first equation.
2y + y = 30
y = 10
now plug your answer into the original equation.
x + 10 = 30
x = 20
hope this helps :)