a)Find the angle at the dish : (6378/sin24)=7358/sinD) --> D= 28. Then find the angle at the centre of the earth : 180-(24+28) = 128.
Distance from the dish to satellite : (x/sin128) = (6378/sin24) --> x = 12357 km
b) 12357/300000 = 0.041 second
Although this answer is correct mathematically, I think the angle in the dish should be an obtuse angle physically , so this is an example of ambiguous case. There are two possible solutions.
If we take D angle obtuse : 180-28 = 152. Then the angle at the center : 180-(152+24) = 4
Distance from the dish to satellite : (x/sin4)= (6378/sin24) --> x = 1094 km
Then the time taken : 1094/300000 = 0.004 second