125 grew only ----------------------wheat
106 grew only-----------------------corn
91 grew only-----------------------oats
198 grew -----------------------wheat
58 grew -----------------------wheat and corn
49 grew -----------------------wheat and oats
172 grew -----------------------corn
we have
corn
106 grew only-----------------------corn
172 grew -----------------------corn
58 grew -----------------------wheat and corn
172-106=66 wheat corn and oats
58 grew -----------------------wheat and corn
66-58=8-------------------------corn and oats
remains
106 grew only-----------------------corn
172 grew -----------------------106 corn +58 wheat and corn + 8 corn and oats
oats
91 grew only-----------------------oats
49 grew -----------------------wheat and oats
wheat
125 grew only ----------------------wheat
198 grew -----------------------wheat
58 grew -----------------------wheat and corn
49 grew -----------------------wheat and oats
198-125=73 wheat, corn and oats
answers
a) Number of farmers who grew at least one of the three
125+106+91=322 farmers
b) Number of farmers who grew all three
66+73=139 farmers
c) Number of farmers who did not grow any of the three
322+58+8+49=437 farmers
d) Number of farmers who grew exactly two of the three
58+8+49=115 farmers