Answer:
6
Step-by-step explanation:
Given the below system of equations;

If we multiply the first equation by 2, we'll have;

To be able to eliminate a variable by adding, we can notice that if multiply Equation 2 by 6. If we do, we'll have;

If we add Equation 3 and 4, we'll have;

So if we multiply the second equation by 6, we will be able to eliminate a variable as seen above.