For each of these circuits, use the branch currents as unknowns and write a set of KCL equations and a set of KVL equations. Arrange your equations into matrix form.
Circuit I: Three KCL equations and three KVL equations.
Circuit II: Three KCL equations and three KVL equations.
Circuit III: Two KCL equations and two KVL equations.
Remark: Do not write mesh equations.