1. The problem statement, all variables and given/known data The question asks me to express the system shown in the image in state-space form, firstly by using the transfer function which was fine but the second part asks to express in state-space form by using the components A,B,C,D as the states x1,x2,x3,x4 2. Relevant equations U(s) = input 3. The attempt at a solution So looking at each branch i got the following: (U(s) - x4)*(4/s+6) = x1 (x1)*(6/s+3) = x3 (x1)*(2/s+2) = x2 these were all correct looking at the mark scheme but for the last branch i did: (x2+x3)*(1/S+1) = x4 whereas the mark scheme says it should be (X1+x2) *(1/S+1) = x4. I dont know why its x1 instead of x3 because looking at the block diagram x2 and x3 are added just before the x4 branch. Can anyone see where i am going wrong?