I hope this makes sense, if not please feel free to let me know and I'll explain it.
The interior angles of a parallelogram will always equal 360. The interior angles of a triangle are 180 if it is a equilateral triangle then the angles are 60 degrees each. You know 2 sides of parallelogram. The 100 degree and 90 degree. You can find the one opposing the x because it’s on a straight line and a straight line is 180 degrees if a triangle is 60 degree angle then the opposing angle to complete the straight line must be 180-60 so you get 120. You now know 3 sides. 120, 90 and 100
They should add up to be 360 so you can set up an equation like so
120+90+100+x=360
And x = 50
Answer:

Step-by-step explanation:
All the angles in a triangle add up to 
Every right angle triangle has a right angle in it which is 
So to find the remaining angle, you do
-
-
= 
Answer:
46 terms
Step-by-step explanation:
a₁=b, a₂₁= bₙ, d₁=9, d₂=4
n=?
---------------
a₂₁= a₁+20d₁= a₁+20*9= a₁+180
bₙ= b₁+(n-1)d₂= a₁+4(n-1)
a₁+4(n-1)=a₁+180
4(n-1)=180
n-1= 180/4
n-1= 45
n=46