If we consider we will get x^3 in the (p+1)th term & x^4 in the (r+1)th term.... The (p+1)th term is nCp 2^(n-p)*3^p*x^p from it we get (p=3) so the co-efficient is nC3 2^(n-3)*3^3.......(1) The (r+1)th term is nCr 2^(n-r)*3^r*x^r from it we can write (x=4) so the co-efficient is nC4 2^(n-4)*3^4.............(2) After doing 1/2 we get (nC3/nC4)*{(2^(n-3)*3^3)/(2^(n-4)*3^4)}=8/15 From it we get 4/(n-3) = 4/5 Or we can write {n=8} .........................................................