I haven't done this in a while (11 years maybe) so I'm just looking at the numbers.
M2S3=4.0g
M2 = .277g
M = .138
S3 = 3.723g
S = 1.274
Atomic weight of S = 32.065
M is 10.8% the weight of S
Atomic weight of M = 3.473??
Probably not right but there is an S3CL2 compound so that's probably the right answer.
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