Let's say that a third/low 2.2 = 50%
0.2(50) + 0.8(y) = 60
50=0.8y
y= 62.5%
Therefore, if you get a 50% in your second year, you'd need 62.5% in your third year to get a 2.1 overall.
Thus, very achievable.
Furthermore, most unis have conventions for awarding classifications independently of the traditional % system, i.e. if you get 58% average but get 4 modules at 60%+ and the other at 50% you can still get a 2.1 overall. But this will depend on your uni's classification rules and best not to rely on this.