Since MO bisects LMN, that means that LMO=LMN and LMO+LMN=LMN (since they add up as shown), meaning that 15x-42=x+56. Subtracting x and adding 42 to both sides, we get 14x=98. Next, we divide both sides by 14 to get x=108/14=7. Adding LMO and LMN up, we get 7*15-42+7+56 (plugging 7 in for x)=21+105=126