For part b$,$ use X$7$ as well and show the code. Also, I think this is the correct code for part a$,$ but you should check if it is correct or not.

ADD X$5,$X$2,$X$1$

NOP

NOP

NOP

LDUR X$3,[$x$5,$#$4]$

LDUR X$2,[$x$2,$#$0]$

NOP

NOP

ORR X$3,$X$5,$X$3$

NOP

NOP

NOP

STUR X$3,[$X$5,$#$0]$