3abc + 5bcd - cda - (cab - 4cad - cbd)
= 3abc + 5bcd - cda - cab + 4cad + cbd
Arrange the polynomial with like terms together and combine them.
= (3abc - abc) + (5bcd + bcd) + (- cda + 4cda)
= 2abc + 6bcd + 3cda
Hence, 3abc + 5bcd - cda - (cab - 4cad - cbd) = 2abc + 6bcd + 3cda.