\[7\ :2\frac{1}{3} + 4\ :1\frac{1}{3} = 7\ :\frac{7}{3} + 4\ :\frac{4}{3} =\]
\[= \frac{7}{1} \cdot \frac{3}{7} + \frac{4}{1} \cdot \frac{3}{4} =\]
\[= \frac{7 \cdot 3}{7} + \frac{4 \cdot 3}{4} = 3 + 3 = 6\]