(2m) (4n) - 3a (2b) - (0,2n) (5m) + b (5a) - 5nm + 8ab =
= 8mn - 6ab - nm + 5ab - 5nm + 8ab = (8mn - nm - 5 nm) + (-6ab + 5ab + 8ab) = 2mn + 7ab.
(2m) (4n) - 3a (2b) - (0,2n) (5m) + b (5a) - 5nm + 8ab =
= 8mn - 6ab - nm + 5ab - 5nm + 8ab = (8mn - nm - 5 nm) + (-6ab + 5ab + 8ab) = 2mn + 7ab.