List all the ports that is available on your monitors.
If they are all vga then
Dvi-i to vga adapter, connect with vga cable
Dvi-d to vga adapter, connect with vga cable
Active dp to vga adapter, connect with vga cable.
Nvidia don't really need a active dp for 3 display setup, but get the active just in case and to save the hassle of passive adapters not working. Also there isn't other choice, when it comes to vga. There are vga to hdmi cables or adapters but i heard they don't work to well or don't work at all.