put n=2^k eq-1
B(2^k) = 3B(2^k/k) + 2^k
B(2^k/k) = 3B(2^k/k^2) + (2^k)/k
B(2^k/k^2) = 3B(2^k/k^3) + (2^k)/k^2
................=3B(2^k/k^x) + (2^k)/k^(x-1)
put 2^k/k^x=2...........eq-2
= 3B(2) + (2^k)/k^(x-1)+...........+ (2^k)/k^2 + (2^k)/k + 2^k
=3*1+(2^k)[1/k^0 + 1/k^1 + 1/k^2+ 1/k^3 +1/k^4 +1 /k^(x-1)] apply g.p formula=a(1-r^n)/1-r
=3+(2^k)[(1-(1/k)^x)/1-1/k]
=3+(2^k) *k*[(k^x-1)]/(k-1) k^x
put k^x=2*2^k from eq-2
=(k.2^K)/(k-1)
put 2^k=n from eq-1
=n.logn is the answer