The sum of the two interior angles is equal to the exterior angle. So angle F + angle E is equals to angle MDE (which is the angle outside) So, F + E = MDE
(5x + 10) + 50 = 12x + 11
5x + 60= 12x + 11 (I combined like terms) 5x + 49 = 12x (I subtracted 11 from both sides) 49 = 7x (I subtracted 5x from both sides) 7 = x (I divide both sides by 7)
Since we are looking for angle F, we replace x for 7 in 5x + 10 So, 5 (7) + 10 = 45 35 + 10 = 45
