7.
[tex]A. \ -14\frac{4}{5}+(-3\frac{4}{5}) = -14\frac{4}{5}-3\frac{4}{5} = -17\frac{8}{5} = -18\frac{3}{5} \ \ \not\in C\\\\B. \ 4-4\cdot2\frac{1}{4} = 4 - 4\cdot\frac{9}{4} = 4-9 = -5 \ \ \in C\\\\C. \ 3 - 4\frac{4}{7} = -1\frac{4}{7} \ \ \not\in C\\\\D. \ -14\frac{2}{5}-7,4 = -14\frac{2}{5}-7\frac{4}{10} = -14\frac{2}{5}-7\frac{2}{5} = -21\frac{4}{5} \ \ \not\in C\\\\Odp. \ B.[/tex]
