d. (1000-dx2-25x4) : 6=143|x6 f. f : 7+25 = [900-(300-48x5) x 9] :9
=1000 - 2d - 100=858|+100 = f : 7+25=(900- 60 x 9):9
= 1000 - 2d=958 =f :7+25=(900-540):9
=1000-958= 2d = f:7+25= 360 : 9
=42=2d = f :7 + 25=40|-25
=2d=42|:2 = f : 7=15|x 7
d=21 f=105