(3a-6b)/(a+b) - (5a-6b)/(a-b) - (4a-5b)/(a+b) - (7a-8b)/(a-b) =(3a-6b)/(a+b) - (4a-5b)/(a+b)- (5a-6b)/(a-b) - (7a-8b)/(a-b) =(3a-6b-4a+5b)/(a+b) - (5a-6b+7a-8b)/(a-b)=-(a+b)/(a+b) - (12a-14b)/(a-b)=-1...