processor has a machine instruction $"$AD $($Ral$),$ R$2"$ that adds the content stored at the memory address held in register R$1$ to the content of Register R$2($The addition result is stored in Register R$2).$a$.$ List and describe the sequence of steps that would have to be carried out under the supervision of the processor's control unit in order to implement this instruction. For each step, the related register $($i$.$e$.,$ PC$,$ MAR, MDR$,$ IR$,$ R$2)$ transfers should be specified. $(10$ points$)$b$.$ How many memory accesses are needed to retrieve and execute this machine instruction? $(5$