How many months after the defeat at Blackheath did Warbeck land at Whitesand Bay?
return the  defeat at  Blackheath ;return Warbeck did land at  Whitesand Bay ;return when  was  #1 ;return when  was  #2 ;return difference of #4 and  #3 in  months
['select', 'select', 'project', 'project', 'arithmetic']