2001*200020002000-2000*200120012001
=2001*2000*100010001-2000*2001*100010001
=0
(91*48*75)/(25*13*16)
=(7*13*16*3*25*3)/(25*13*16)
=(7*3*3)*(25*13*16)/(25*13*16)
=7*3*3
=63