Make me less of an idiot and help me not blow up PC

Upgraded GPU. New GPU needs 14 total pins, I only have one 6+2 cable. I bought cable linked below hoping to plug in next to stock PCIe cable to supply the additional 6 pins. The cable is described as "PCIE Cable for EVGA, PCIe 8 Pin Male to Dual PCIe 8 Pin (6+2) Male GPU Power Cable for EVGA". After doing research, I realized I may be stupid. Here are my questions:

a) Can I plug this directly into my PSU and just use 6 pins?

b) If not, can I plug it into my stock 6+2 cable and power both GPU connectors from one PSU connector?