Question : Adding a sata drive

I have a Dell Optiplex 745 which has two SATA slots on the mother board, I want to add another sata drive. IThe moterboard has three PCI slots one is the standard 8.5cm long  one is 11cm long and the other is I think a PCI express slot. What si teh best way of acheiving this?  
thanks

Answer : Adding a sata drive

Are the 2 sata slots already used? if not, mount the second sata and plug it into the open sata port.

I assume both sata slots are filled, since you mentioned the pci slots, you could get an add in card to give more slots. Here is an example.
https://www2.insight.com/search/ppp.web?fromSearch=true&materialId=PEXSATA22I

Thanks