First all the angles add up to 360°. You would subtract 180 from the 360 because of the 2 right angles. That leaves you with 180. Then 180-102.3 to get 77.7°, your answer.
If the perimeter is 28 units, then you know you will have to add the same four numbers to get the perimeter. What times 4 can get you to 28? 7. 7 x 4=28. So what plus 3 gets us to 7? 4. The answer is 4, or x=4.
