Answer:
f = 22
Step-by-step explanation:
The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.
140° is an exterior angle of the triangle, thus
4f + 1 + 51 = 140, that is
4f + 52 = 140 ( subtract 52 from both sides )
4f = 88 ( divide both sides by 4 )
f = 22
