a)$\frac{3}{12}$ x$\frac{4}{11}$ =$\frac{3x4}{12x11}$ =$\frac{1}{11}$
b)$\frac{6}{13}$ :$\frac{26}{39}$ =$\frac{6}{13}$ x$\frac{39}{26}$ =$\frac{6x39}{13x26}$ =$\frac{9}{13}$
c)$\frac{67}{125}$ x3=$\frac{67x3}{125}$ =$\frac{201}{125}$ =1$\frac{76}{125}$
d)12:$\frac{36}{47}$ =12x$\frac{47}{36}$ =$\frac{12x47}{36}$ =$\frac{47}{3}$ =15$\frac{2}{3}$