Answer:
x = 6
Explanation:
3x + 6y = 24 <--- This is the original equation.
3(6) + 6y = 24 <--- Replace the variable.
18 + 6y = 24 <--- Simplify
24y = 24 <--- Do the addition.
24 = 24 <--- This equation is correct.
Therefore, x = 6.
I hope his helps! :D