Answer:
I can't give a full answer because I can't see the image whilst giving an answer but I'll try so....
Explanation:
Angles in a straight line add to 180° so when you have one of two of them angles are them together and take away from 180°
Angles around a full point add to 360° so add angles together and take away from 360°
On A I think it is you have a 360° angle and have to work out 3 and you have one already done and the opposite angle is the same as that so you basically have two angles then you add them together then take from 360 then divide the answer by two and then that would be the angles for a and x
And for the last one you have been given two angles with a right angle and a right angle equals 90 so add them together and take from 180 to get the missing angle
Hope this helps :)