Where can I find the formula to solve this exercise :

```
(def lookup
{:mercury 0.2408467
:venus 0.61519726
:earth 1
:mars 1.8808158
:jupiter 11.862615
:saturn 29.447498
:uranus 84.016846
:neptune 164.79132})
(defn convert-space-age
[age source-planet target-planet]
)
```

What exercise? What exactly needs to be done?

it is this exercise : Clojure Camp Exercises

There’s a solution right on that page, in the expandable section at the bottom.

It’s the bulk of the exercise to come up with the formula, so there’s no much difference between posting a formula and posting a full solution.

The solution is just the rule of three. Nothing else. You have to do that exercise on a piece of paper first like in school to see that this is the solution.