It's just an enlarged version of the 16-bit division. There's not enough unused page-zero locations on a C64 to have all the variables in page-zero. The remainder variable is in page-zero because is the most used.
<code>
; Executes an unsigned integer division of a 24-bit dividend by a 24-bit divisor
; the result goes to dividend and remainder variables
;
; Verz!!! 18-mar-2017

div24	lda #0	        ;preset remainder to 0
	sta remainder
	sta remainder+1
	sta remainder+2
	ldx #24	        ;repeat for each bit: ...

divloop	asl dividend	;dividend lb & hb*2, msb -> Carry
	rol dividend+1	
	rol dividend+2
	rol remainder	;remainder lb & hb * 2 + msb from carry
	rol remainder+1
	rol remainder+2
	lda remainder
	sec
	sbc divisor	;substract divisor to see if it fits in
	tay	        ;lb result -> Y, for we may need it later
	lda remainder+1
	sbc divisor+1
	sta pztemp
	lda remainder+2
	sbc divisor+2
	bcc skip	;if carry=0 then divisor didn't fit in yet

	sta remainder+2	;else save substraction result as new remainder,
	lda pztemp
	sta remainder+1
	sty remainder	
	inc dividend 	;and INCrement result cause divisor fit in 1 times

skip	dex
	bne divloop	
	rts

dividend 	.ds 3
divisor 	.ds 3
remainder 	.equ $fb	; remainder is in zero-page to gain some cycle/byte ($fb-$fd)
pztemp 	 	.equ $fe

</code>