We can solve this also in a different way.
See 2, 4 8, 16..... can be written as
010000...(x times 0 depend upon the number)
i.e
2 = 010
4 = 0100
8 = 01000
16=010000 and so on.
So now if any number Y multiply with any of the above the answer will be Y followed by x times 0.
i.e.
if any number say 7 is multiplied with 16 answer will be
1110000.
So number of 1 will be the number of 1 in that number as multiplication with 2, 4 8 ,6.... can only increase 0 on it.
So number of 1 in
16^3∗9+16^2∗7+16∗5+3
is equal to
number of 1 in 9+
number of 1 in 7+
number of 1 in 5+
number of 1 in 3
=2+3+2+2
=9