Выразим x:
$$x = 7\frac{1}{6} - 4\frac{2}{9} = \frac{43}{6} - \frac{38}{9} = \frac{43 \cdot 3}{6 \cdot 3} - \frac{38 \cdot 2}{9 \cdot 2} = \frac{129}{18} - \frac{76}{18} = \frac{53}{18} = 2\frac{17}{18}$$Ответ: $$x=2\frac{17}{18}$$
Выразим y:
$$y = 15 : 0,025 = 15 : \frac{25}{1000} = 15 \cdot \frac{1000}{25} = 15 \cdot 40 = 600$$Ответ: y = 600
Выразим z:
$$z = 1,5 - \frac{5}{12} = \frac{3}{2} - \frac{5}{12} = \frac{3 \cdot 6}{2 \cdot 6} - \frac{5}{12} = \frac{18}{12} - \frac{5}{12} = \frac{13}{12} = 1\frac{1}{12}$$Ответ: $$z = 1\frac{1}{12}$$
Выразим t:
$$(7,4-t) \cdot 2,4 = 6$$ $$7,4-t = \frac{6}{2,4}$$ $$7,4-t = \frac{60}{24}$$ $$7,4-t = \frac{5}{2}$$ $$7,4-t = 2,5$$ $$t = 7,4 - 2,5 = 4,9$$Ответ: t = 4,9