б) $$5\frac{1}{4}y - 5\frac{1}{4} = 1$$
$$\frac{21}{4}y - \frac{21}{4} = 1$$
$$\frac{21}{4}y = 1 + \frac{21}{4}$$
$$\frac{21}{4}y = \frac{4+21}{4}$$
$$\frac{21}{4}y = \frac{25}{4}$$
$$y = \frac{25}{4} : \frac{21}{4}$$
$$y = \frac{25}{4} \cdot \frac{4}{21}$$
$$y = \frac{25 \cdot 4}{4 \cdot 21}$$
$$y = \frac{25}{21} = 1\frac{4}{21}$$
Ответ: $$1\frac{4}{21}$$