Concept
Sum of all interior angles in any polygon = (n - 2) x 180 degrees
Next,
Add all the interior angles and equate it to (n - 2) x 180
Where n is the number of sides or angle.
From the diagram, n = 7 Heptagon
Substitute n = 7 in the equation
Therefore we get
118 + w + 120 + 147 + 99 + w + w = (7 - 2) x 180
3w + 484 = 5 x 180
3w + 484 = 900
Final