They both take 17.1 min to make the pizzas.
Explanation:
Ron can do a job in 30 mins =

Jeff can do a job in 40 mins =

They both work together =

We have to take LCM of 30 and 40 as 120, so that the denominator becomes equal, also we can add them.
=

Further we get,

They both work for 17 .1 mins to make the same number of pizzas.