Supposing total number of dogs in the sample n = 100 as it makes converting percent in numbers(frequency) easier.
This means that there are 5 dogs weighing 7kg, 10 dogs weighing 8 kg, 20 dogs weighing 9 kgs, 10 dogs weighing 10 kgs and 10 dogs weighing 11kgs and likewise.

if you add number of dogs till 10kgs we get 45 dogs (5+10+20+10), 55 dogs (45+10) that weigh up till 11 kgs.

As median weight is the weight of 50th dog, so median has to be among the 10 dogs that weighed 11. So median is 11 kgs.


For mean weight, you can sum the product of weights with number of dogs for all weights classes divide by 100.
i.e. (7*5+8*10+9*20+10*10+11*10+121*5+13*25+14*10+15*5)/100= 1105/100 = 11.05

Since, 11 < 11.05. Therefore Quantity B