Basculin is worth 2 Speed EVs, and Macho Brace doubles EV count. Pokerus stacks with Macho Brace/Power items, and also doubles EV count. So each Basculin would be worth 2*2*2, or 8, Speed EVs. Each Carbos is worth 10 Speed EVs. If you give a Pokemon 10 Carbos (10*10 = 100), and you want 252 Speed EVs, 252-100 is 152. 152/8 is 19. So you will have to defeat 19 Basculin.

If you use the Power Anklet, though, it puts +4 Speed EVs on whatever it is that you're fighting, so Basculin would be (2+4)*2, or 12, EVs each. 152/12 = 13 Basculin that you would have to fight.

I'm not sure how many EVs you want to put into Attack, so I'm assuming it's 252 again. So you give your Pokemon 10 Proteins (10*10=100 Atk EVs), and 252-100 = 152 EVs left. Then you are fighting Patrat/Lillipup, and those are worth 1 Atk EV each. You have a Macho Brace and Pokerus. 1*2*2 = 4, so each Lillipup/Patrat is worth 4 Attack EVs. 152/4 = 38 Patrats/Lillipups that you have to fight.

If you used the Power Bracer, each Patrat/Lillipup would be worth (1+4)*2, or 10, Attack EVs. So then you would only have to fight 152/10, or 16, Lillipups/Patrats.