$$12-3 \frac{8}{11} = 11 \frac{11}{11} - 3 \frac{8}{11} = (11-3) + (\frac{11}{11} - \frac{8}{11}) = 8 + \frac{11-8}{11} = 8 + \frac{3}{11} = 8 \frac{3}{11}$$.
Ответ: $$8 \frac{3}{11}$$