Применим правило умножения крест накрест:

x : 1/3 = 3/4 : 1/27;

x * 1/27 = 3/4 * 1/3;

x * 1/27 = 1/4;

x = 1/4 : 1/27;

x = 1/4 * 27/1;

x = 27/4;

x = 6 3/4.