420% – 7:10.5 x 33/4​

10.5 = 105/10

420% – 7:10.5 x 33/4

= 420/100 – 7/105 x 10 x 33/4

= 42/10 – 70/105 x 33/4

= 21/5 – 14/21 x 33/4

= 21/5 – (14 x 33)/(21 x 4)

= 21/5 – 462/84

= 21/5 – 66/12

= 21/5 – 22/4

= 21(4)/(5 x 4) – 22(5)/4(5)

= 84/20 – 110/20

= – 26/20

= – 13/10

= -1,3