\[\boxed{\mathbf{841\ (841).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ \frac{8a^{2}c^{3}}{4a^{3}c^{2}} = \frac{2c}{a}\]
\[2)\ \frac{25mn²}{75m^{8}n} = \frac{n}{3m^{7}}\]
\[3)\ \frac{60a^{3}bc^{2}d^{5}}{18a^{4}b^{2}c^{6}d} = \frac{10d^{4}}{3abc^{4}}\]
\[4)\ \frac{42x^{8}y^{9}}{14x^{6}y³} = \frac{6x^{2}y^{6}}{2} = 3x^{2}y^{6}\]