A study of the yield of 150 tomato plant resulted in the record. Calculate the mean of the following a number of tomatoes per plant.
Tomatoes per plant No. of plants
1-5 20
6-10 50
11-15 46
16-20 12
21-25 12

a) 11.53
b) 15.76
c) 12.42
d) 11.00