For readablity reasons logically group your -export(..) declarations.
At most one -export(..) block per group, where group can be (in this order):

Export one function per line at least for the public API (except for same name function of different arities)

    %% API
    -export([
      add/2,
      divide/2,
      increment/1, increment/2,
      mult/2,
      substract/2
    ]).