4^m*8^(m-1)*2^(m-1)=256
(2^2)^m*(2^3)^(m-1)*2^(m-1)=2^8
2^2m*2^(3m-3)*2^(m-1)=2^8
2^(6m-4)=2^8
6m-4=8
6m=12
m=2