Calculate DOI and identify the following structure as determinate, indeterminate, or unstable. Your answer is DOI if determinate or indeterminate and "-1" if unstable (the answer for any unstable structure is "-1" irrespective of the value of DOI).

Question 1: The rectangular rigid-bar-assemblage shown in the figure below consists of three rigid bars interconnected by frictionless hinges. The horizontal displacement at joint 3 is resisted by a translational spring of stiffness ki and the rotation at joint 4 is resisted by a rotational spring of stiffness kr. Determine the buckling load Per and the nature of the equilibrium state (i.e., the load range at which the equilibrium state is stable and unstable, respectively). Dimensions are shown in the figure (width: a; height: h). ww