$($a$)$ Design an automatic vending machine. The candy bars inside the machine cost $3Tk,$

and the machine accepts $1Tk$ and $2Tk$ only. An electromechanical system accepts the

coins sequentially. The circuit produces a level output that delivers the candy whenever

the amount received by the machine is $3Tk$ or more. The excess amount is kept

deposited for the next candy. Design a pulse mode circuit for the vending machine using

S$-$R flipflops. Draw the circuit diagram.