\[\begin{aligned} A &= \frac 2 7 \times \frac 9 4 = \frac 1 7 \times \frac 9 2 =\frac{9}{14}.&\\ B &= 5 \times \frac 7 {15} = \frac 7 3.&\\ C&=\frac{36}{35} \times \frac{21}{12} =\frac{3}{5} \times \frac{3}{1} = \frac{9} 5.& \end{aligned}\]