Question

a man weight 1645n,what is his mass

Answer 1

Weight=Mass x g=Mass x 9.8
Mass=weight/9.8

Answer 2

Weight G = mg, in which g = 9,80665 m/s\[^{2}\]
m = G/g = 1654 N / 9,80665 m/s2 = 168,66106 kg
Also with exact accuracy mass is 168,7 kg.

Notice that you have to use more accurate value for g as usual.

Answer 3

M = w/g = 167.7kg

Answer 4

Do u mean "his mass" on earth or moon or Jupiter bcoz g varies with planet :)
for the earth above mentioned is correct :)