To solve this, you would want to subtract DXC from DXB. This would be 70°15'12"-30°30'20". First, you would subtract the seconds. 12"-20"=-8". As there are 60 seconds per minute, this -8" becomes 52" and the minutes go down by one. This makes your problem become 70°14'52"-30°30'. Now, you subtract the minutes, 14'-30'=-16'. As there are 60 minutes per degree, you lower your degree by 1 and turn -16' into 44'. This leaves you with 69°44'52"-30°. Lastly, you subtract the degrees 69°-30°=39°. This leaves you with 39°44'52" as your value of angle CXB. In the first box, you'd write 39, 44 in the second, and 52 in the last.
