I would greatly appreciate help with steps please.

A research reactor is fueled by natural $($unenriched$)$ uranium, In one experiment, it is observed that for every $1000$ neutrons absorbed in $235$U$,251$ fast neutrons are absorbed in resonances of $238$U and $644$ thermal neutrons are absorbed by $238$U$.$ There is essentially no leakage of neutrons from the reactor.

$($a$)$ What is the conversion ratio for this reactor?

$($b$)$ How much $239$Pu is produced when $1$ kg of $235$U is consumed?