Look at the parallelogram below. Ð1 and Ð3 are each 35°.

Ok so for paralellograms

1. all angles inside are adding up to 360

2. opposite angles are congruent

3. adgacent angles are adding up to 180

so

D2=D4

D1=D3=35

D2+D1=180

D2+35=180

D2=145

D2=D4

D4=145

D4=D2=145 degrees

A parallelogram has four sides having 90 degrees at each corner and the total sum is 360 degrees. When you have a parallelogram that has an angle of 35 degrees at D1 and D3, summing the two angles you will have 70 degrees. Subtract 360 by 70 and you will get 290. Then divide it by 2 and you will get an angle of 145 degrees at D2 and D4