Pleaseee helpp answer correctly !!!!!!!!!!!!!!! Will mark Brianliest !!!!!!!!!!!!!!!!!!!!

Answer:
4
Step-by-step explanation:
In a parallelogram AO and OC are equal. Therefore you should set up the equation 3x-4=8. When you add 4 to both sides you get 3x=12. When you divide both sides by 3 you get x=4