(8/3) ohms in parallel.
12 ohms in series
By the way, if you don't know the formula, you can just figure it out using google or a search engine.
Series: Just add em up
Parallel: Where R1 = Resistance of first speaker, and R2 = Resistance of second speakers, it looks like this.
(1/R1) + (1/R2) = (1/RT) Where RT = Total Resistance.
This is an elementary formula that anyone with an interest in car audio should be aware of. There's no need for a thread about it.