There are 10 boatmen in a boat. After replacing a 56 Kg boatman with a new boatman

There are 10 boatmen in a boat. After replacing a 56 Kg boatman with a new boatman the average weight of boat is increase 800 gm. What is the weight of the new boatman?
(a) 8 Kg.
(b) 9 Kg.
(c) 64 Kg.
(d) 56 Kg.