Question

5k=-84.05 can you help me find k?

Answer 1

Yes indeed !  You've come to the right place.

You said that                      5k  =  -84.05

Now, watch closely:

Divide each side by  5 :    k  =  -16.81 .
 

Answer 2

84.05/5=k

You need to do the inverse operation of multiplication which is division 

So you need to divide