Найдите от числа 28: 1) 1/2 ; 2) 3/7; 3 ) 9/14; 4 ) 19/28

Решите задачу:

$28* \frac{1}{2} = \frac{28}{1} * \frac{1}{2} =\frac{28:2}{1} * \frac{1}{2:2} =\frac{14}{1} * \frac{1}{1} =14 \\ \\ \\ \frac{28}{1} * \frac{3}{7} =\frac{28:7}{1} * \frac{3}{7:7} =\frac{4}{1} * \frac{3}{1} =\frac{4*3}{1} =\frac{12}{1} =12 \\ \\ \\ \frac{28}{1} * \frac{9}{14} =\frac{28:14}{1} * \frac{9}{14:14} =\frac{2}{1} * \frac{9}{1} =\frac{2*9}{1} =18 \\ \\ \\ \frac{28}{1} * \frac{19}{28} =\frac{28:28}{1} * \frac{19}{28:28} =\frac{1}{1} * \frac{19}{1} =19$