Question

Three angles ofa quadrilateral are 60', 75' and 100'.
Find the fourth angle. Also, find all the four extemal
angles.

Answer 1

Sum of the 4 angles of a quadrilateral = 360 degrees

sum of the given three angles 60, 75, 100 is equal to 235

The fourth angle = 360 – 235 = 125 degrees 

Answer 2

∠1=60°
∠ 2=75°
∠3=100°
let  ∠4=x
since the sum of all interior angles of a quadilateral=360°
ATQ
60° + 75° + 100° + x = 360°
235° + x = 360°
x = 360° - 235°
x = 125°


FINDING THE EXTERIOR ANGLES-
linear pair = 180°
∠1=60° 
∴ exterior ∠1 = 180° ⁻ 60°
= 120°
∠2 = 75°
 ∴ exterior ∠2 = 180° - 75°
= 105°
∠3 =100°
∴ exterior ∠3 = 180° - 100°
= 80°
∠4 = 125°
∴ exterior ∠4 = 180° - 125°
= 55°
as we know that the sum of exterior angles of a quadilateral equal to 360°
thus, 120° ⁺ 105° + 80° + 55° = 360°

ps.- you can completely rely on this answer. happy to help. :))