Maths (Average num)

number of leaves of a tree
=number of branches x number of leaves in each branch
therefore
the average number of leaves of a tree
=average B branches x average n leaves in each branch
=Bn
=B(7B^2-B)
=B^2(7B-1), since B=y-6
=(y-6)^2[7(y-6)-1]
=(y-6)^2(7y-43)
=(y^2-12y+36)(7y-43)
=7y^3-127y^2+768y-1548

Average number of leave of a tree
= 7B2 - B
= 7(y - 6)2 - (y - 6)
= 7(y2 - 12y + 36) - (y - 6)
= 7y2 - 84y + 252 - y + 6
= 7y2 - 85y + 258
=