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
I hope this helps.
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