How to get my mom to let me...?

how can i get my mom to let me hang out at my brothers apartment at college for a weekend? im 14 and ive been talking to my older bro who is 19 about chilling at his place for a weekend cause we never get to see each other. his place is about an hour and a half away.which isnt a big hassle for her. we have been trying to convince my mom that it was ok to let me go there but she keeps making up excuses to not let me go. me and my older bro have a history of drinking and smoking weed together..so this might be a factor but we weren't planning on doing any drugs we just want to hang out.she always tells me to get out of the house and stuff(i live in a rural area) but what am i supposed to do? and whenever i bring this up she makes up an excuse..like im not feeling well or maybe next week. its like wtf chick!