Answer:
I'm not sure what you mean by "make the subject."
I can only guess that you'd like to solve this equation for r, which might be what you're looking for.
By "solve this equation for r," what I mean is to rewrite it in the form "r = [some expression]."
This is also known as "isolating." By performing operations on both sides of the equation the task is achieved.
Step-by-step explanation:
In your example we could begin by dividing both sides by 2, as demonstrated below.
d = 2r
d / 2 = (2r) / 2
d / 2 = r or reversing the equality
r = d / 2.
That didn't require many operations, but the idea is the same for more complicated equations.
Hope this helps.
