Using half-adders and full-adders as a block together with external gates, design the following circuit in the most efficient way possible. (20 p.) S = K - L + M - N (K, L, M and N are 3-bit numbers and should be represented as KzKKo, L2L1L0, M2M Mo and N2N1No) Using half-adders and full-adders as a block together with external gates, design the following circuit in the most efficient way possible. (20 p.) S = K - L + M - N (K, L, M and N are 3-bit numbers and should be represented as KzKKo, L2L1L0, M2M Mo and N2N1No)