The chips are arranged in 4x6 array, each chip is powered with 8kx4 bits.
=4x6x 8 x k x 4 //1k=2^10
=4x6x2^3x2^10x2^2
=2^2x6x2^3x2^10x2^2=2^17x6
need 2^20 lines but storage is a type of byte not bit so, divide by 8
2^20/2^3
=2^17
so 17 lines are needed