Electronic – Divisible-by-2 Circuit Help!

The way the truth table was filled is the following: You make a list of all the possible states and inputs, in this case A-D in with their respective mapping and X either 0 or 1 for this case. This should cover columns y1,y2 and X. Then we reference the first table, Which tells me that for State A[y1=0,y2=0]and X=0, my next state should be D[Y1=1,Y2=1] and my output Z, and so on and so forth until you go through all the possible states and input combinations

Here's a hint: The states in your state machine are not associated with the binary codes representing the key inputs, they're associated with the number of correct numbers entered so far. You start out in an initial, or "reset" state, in which no valid keys have been entered so far, and then proceed to states representing 1 valid key entered, 2 valid keys entered, etc. until you get to the final state with 5 valid keys entered. In the last state, the output is 1; in all others it's 0.

In each state, if the next valid key is entered, you proceed to the next state; otherwise, you go back to the initial state.