I'd suggest to use readtable instead, first...
T = readtable('studentmarks.txt');
presuming the above format string is correct for the file content.
Without a header line in the file, the default variable names will be Var1 through VarN, you can make use of meaningful names by assigning them in T.Properties.VariableNames.
See the doc on the table class for all the syntax...
The Q? answer specifically is to use sum() with the second optional input argument to tell it to sum rows instead of columns.