We are given

Since, this is equation of ellipse
so, firstly we will change it into standard equation of ellipse

now, we can change our equation into this form

we divide both sides by 36
we get

now, we can simplify it

now, we can compare and find 'a' and 'b'

Since, shorter value is b
so, length of minor axis is 2b
length of minor axis is 2*3
The length of minor axis is 6...........Answer