Answer:

' Number of Winter Days
'
PRINT "Winter Days = ", 11 + 31 + 28 + 19
END

When all the operators are the same, start at the left and do the arithmetic one operator at a time. Doing this for the above:

 11 + 31 + 28 + 19    42 + 28 + 19  70 + 19   89
--------                 --------          -------
do first                 do second         do third