Answer:
By "make k as a subject", I assume you mean to solve for k?
If that is the case, then the answer is:
k = (c - a) / b
Explanation:
Let's solve for k
a/k + b = c/k
Multiply both sides by k:
a + bk = c
Group terms containing k on the left:
bk = c - a
Divide both sides by k:
k = (c - a) / b