For each of the following two systems, we want to separate the variables into exogenous and endogenous ones so that each choice of values for the exogenous variables determines unique values for the endogenous variables. For each system, a) determine how many variables can he endogenous at any one time, b) determine a successful separation into exogenous and endogenous variables, and c) find an explicit formula for the endogenous variables in terms of the exogenous ones:
x+2y+z-w=1
3x-y-4z+2w=3
y+z+w=0