10 is the correct answer
the max no of keys are inserted in each level
level 1 -- > Root ---- > 2 keys
level 2 ---> 3 x 2 keys
level 3 ---> 3 ^2 x 2 = 18 keys
Order of lead node = 2
it means 9 such node can be present in the leaf node each have order 2
out of 18 keys only 8 keys are filled up which are : (13,15,21,29,37,42,51,68)
18- 8 = 10 [we can inserted 10 more keys into the leaf node ]