ONLY 1 rca output for subwoofer connection?

Hi, maybe one of you can help me, I have a Insignia car cd player I bought at Best Buy. I bought it because it was only $99 installed and it had 3 sets of rca`s for amp hook ups. I went to hook up a subwoofer amp and the 1st set of rca`s said for: Front left & right speakers and the 2nd set of rca`s said : For left & right rear speakers and NOW my question: There is ONLY ONE rca for the Subwoofer and the single rca says: Subwoofer . Now I ran my rca`s from my amp, but since I have 2 rca`s from the amp how do I connect it to the decks one subwoofer rca? Anybody got any idea`s? Thanks....PJ