21, 13*(-6,07) + (-11, 13)*(-6,07) =

21*(13/24-7/12-1/6)=-4,375

13/24-7/12=13/24-14/24=-1/24

-1/24-1/6=-1/24-4/24=-5/24

21/1*(-5/24)=-105/24=-4,375