For the circuit of Figure $2$:

a$)$ If $V_A=0,V_B=1,R_A=R_B=10k,R_1=70k,R_2=,$ and $v_{\text{o}\text{u}\text{t}}=8V,$ which terminal $(A$ or $B)$ is the noninverting input? Explain.

b$)V_A=10,V_B=0V.$ If $B$ is the inverting input, select $R_A,R_B,R_1$ and $R_2$ obtain an output voltage of $20V.$

c$)V_A=V_B=1V,R_1=0,$ and $R_2=.$ If $V_{\text{o}\text{u}\text{t}}$ is found to be $1V,$ which terminal $(A$ or $B)$ is the inverting input? Explain.