First, you'd subtract the 7 from both sides of the equal sign. This would cancel out the seven on the left (7-7=0) and turn the 8 on the right into a 1 (8-7=1).
You'd now be left with:
\(\frac{k}{4}\) = 1
If you were to multiply k/4 with 4, it would cancel out the 4 there, leaving just the k. Of course, you'd have to do the same thing with the 1 on the right.
1 x 4 = 4
And so, k = 4
