Sorry if it looks bad I did it in the car xd. You would multiple 6 with 7 and you would get 42 then you would multiply 6 with -10 and you would get -60 then you'd bring down the = 24 and it would look like 42k-60=24 then add 60 to 24 and you'd get 84 then you'd divide 84 by 42 and get 2 so then you would get k=2
