Correct question is;
1/0.12 = (1/0.05) + (1/d')
Answer:
d' = -1/700
Explanation:
1/0.12 = (1/0.05) + (1/d')
Let's rearrange to get;
(1/d') = (1/0.12) - (1/0.05)
(1/d') = (1/(12/100)) - (1/(5/100))
(1/d') = 100/12 - 100/5
Let's multiply through by 60 to get rid of the denominators on the right side;
> (1/d') = 500 - 1200
> (1/d') = -700
> d' = -1/700
