How many years after the region became a British protectorate in 1891, was it named Nyasaland?
return the  region became a British protectorate in  1891 ;return the  region was  named Nyasaland ;return year of #1 ;return year of #2 ;return difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']