Missing clarification of result

[favetelinguis]

Hi, how am I to interpret this result in lay man terms (im not a math wiz)?

(def t (sym/ex (= t 30000))) (def t1 (sym/ex (= t (+ a b c)))) (sym/solve '[a b c] t t1)

{{a (+ (* -1 (+ _0 _1)) 30000), c _0, b _1}}

The _0 is explained in the tutorial as being any number but what is _1? Also how can i make a constraint that a b and c must be >0?

Thanks for a really fun library, hope you continue working on it for a long time :)