As the exponent 10 is even, so the middle term of the expansion
[

x

3

+9y]10 is [

10

2

+1] th term i.e., 6th term which is given by
T6 = T5+1 =

10

‌

C5(

x

3

)10−5(9y)5 = (252) (

x

3

)5(9y)5 = (252)

95

35

x5y5
= (252) 35x5y5 = 61236 x5y5