Question

Make "z" the subject of:

a/z = d

Answer 1

I'm not familiar with the terminology of "making the subject of"

However, it seems natural that it would mean to isolate a variable on one side of an equation. If that's the case, then you can simply multiply both sides by z to get
a = z*d
then divide both sides by d to get
a/d = z

Answer 2

Makes sense, thank you !

Answer 3

My pleasure =)