Let us assume that Timmy and Jared are eating 2 cupcakes combined. As it is not given if they are eating 2 each.
Time taken by Timmy and Jared to eat 2 cupcakes = 3 minutes
Time taken by both of them to eat 18 cupcakes in =
=27
Hence, Timmy and Jared can eat 18 cupcakes in 27 minutes.