упростить 5/7(2,8c-4 1/5d)-2,4(5/6c-1,5d)

Convert fractions and decimals: 5/7(14/5c - 21/5d) - 12/5(5/6c - 3/2d).
Distribute: 2c - 3d - 2c + 18/5d.
Combine like terms: (2c - 2c) + (-3d + 18/5d) = 0c + (-15/5d + 18/5d) = 3/5d.