Answer:
n = 9
Step-by-step explanation:
The sum of the interior angles of a polygon is
sum = 180° (n - 2) ← n is the number of sides
Given 3 angles and the remaining angle of 141° then there are
141(n - 3) angles of this size
Then
99 + 153 + 162 + 141(n - 3) = 180(n - 2) , that is
414 + 141n - 423 = 180n - 360
141n - 9 = 180n - 360 ( subtract 141n from both sides )
- 9 = 39n - 360 ( add 360 to both sides )
351 = 39n ( divide both sides by 39 )
9 = n
The polygon has 9 sides
