a$)$ Assume you want to organize a nested subroutine calls on a computer as follows: the routine 'main' calls a subroutine 'SUB$1\text{'}$ by executing a two$-$word call subroutine instruction located in memory at address $1000$ followed by the address field of $6000$ at Iocation $1001.$ Again subroutine 'SUB$1\text{'}$ calls another subroutine 'SUB$2\text{'}$ by executing a two$-$word call subroutine instruction located in memory at address $6050$ followed by the address field of $8000$ at location $6051.$ The content of the top of the memory stack $($ToS$)$ and stack pointer $($SP$)$ is $5000$ and $3000$ respectively. What are the content of $PC,SP,$ and Top of the stack $?$

i$)$ After the subroutine call instruction is executed in the 'main' routine?

ii$)$ After the subroutine call instruction is executed in the subroutine 'SUB$1\text{'}?$

iii$)$ After the return from 'SUB$2\text{'}$ subroutine?