How many months after being flown in the testbed did the V-1710-C6 successfully completed the USAAC 150 hour Type certificate?
return the  V-1710-C6 was  flown in  the   testbed ;return the  V-1710-C6 successfully completed the   USAAC 150 hour Type certificate ;return when  was  #1 ;return when  was  #2 ;return difference of #4 and  #3 in  months
['select', 'select', 'project', 'project', 'arithmetic']