Answer :
you have to add 1 to the -1 and you will get 0.What you have to do next is also add 1 to 15 because you want a variable on one side and a number on the other.So now you have 8k=16. So you divide 8 to 8k and you get nothing divide 8 and 16 and your answer for k =2 hope you get it right.trust mw it is very easy when you get use to it
[tex]8k-1=15\ \ \ \ /+1\\\\8k-1+1=15+1\\\\8k=16\ \ \ \ /:8\\\\8k:8=16:8\\\\k=2[/tex]