7seg with decoder

Huy guys,

I need your help...
I have arduino mega 2560,nine 7seg...
I need to separate three 7seg per group
In total i have 3 groups

My question is:
How many decoder i need?
(i try to reduce pins)

Thanks in advance

The available options for me (assume multiplexed display unit):
(1) (8+9) IO lines, 3x3 cc-type 7-segment display devices, and no extra decoder
(2) (8 + 4) IO lines, 3x3 cc-type 7-segment display devices, and one 74LS154 decoder
(3) (5 + 4) IO lines, 3x3 cc-type 7-segment display devices, one 74LS259 latch, and one 74LS154 decoder

But you are using Arduino MEGA; it has a lot of IO lines; you can go for option-1.