any pci or pci-e video card.
such as ATI Radeon video cards (not agp ones) or NVidia GeForce video cards (again, excluding the agp ones)
No sorry the Dell Optiplex 780 can't support a i7, it would have to be a 1155, 1156, 1366 socket compatible motherboard, but your options would be a Intel Core 2 Quad like a Q6700, upwards. Your Dell has a 775 socket.
280 + 500 = 780
780
780
35% of 780= 35% * 780= 0.35 * 780= 273
45% of 780= 45% * 780= 0.45 * 780= 351
150% of 780= 150% * 780= 1.5 * 780= 1170
55% of 780 = 55% * 780 = 0.55 * 780 = 429
780
78
The multiples of 780 (which are infinite) are all divisible by 780, including these: 780, 1560, 2340, 3120, 3900, 4680, 5460 . . .
13 x 60 = 780