$(25$ pts$)$ a$)$ What is the purpose of the following program? b$)$ After the following program is executed what are the contents of $A,B,$ and $R5$ in hex?

MOV R$4,$ #$5$

MOV $A,R4$

DEC R$4$

MOV $B,R4$

MUL $AB$

DJNZ R$4,$ NEXT

MOV R$5,$ A

END

ACC$=$

$B=$

$R5=$