Suppose that an initially empty stack performs (in some order) 18 push operations, 8 peek operations, and 12 pop operations. 3 of the peek operations and 5 of the pop operations return null, indicating that the stack is currently empty. After all of these operations, how many items are in the stack?

Refrigerant 134a enters an insulated compressor operating at steady state as saturated vapor at -26°c with a volumetric flow rate of 0.18 m3/s. refrigerant exits at 9 bar, 70°c. changes in kinetic and potential energy from inlet to exit can be ignored. determine the volumetric flow rate at the exit, in m3/s, and the compressor power, in kw.