Between British blockading of French ports in 1755 and formal declarations of war in the following spring, how many years separated these events?
return the  British blockading of French ports in  1755 ;return formal declarations of war in  the  following spring ;return year of #1 ;return year of #2 ;return the  difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']