treatment of foreign exchange loss

Dear sir,

A company has purchased $500 for Rs25000 (rate is Rs 50 per dollar) gave to the employee as foreign travel advance, after completion of his travel he returned $100 dollar to the company (rate as on that date is Rs45) could you clarify me which entry is true??????? give reasons and on which basis???????

(a)  Foreign travel expences a/c  Dr   20,000   ($400*Rs50=Rs20,000)

      Bank a/c Dr                          Dr   4500     (assuming $ has converted into rupees                                     

                                                                        100*45=4500)

      Foreign exchange loss        Dr     500        (100*5=500)

      Foreign travel advance        Cr      25,000

(b)  Foreign travel expences a/c  Dr   18,000    ($400*Rs45=Rs18,000)

      Bank a/c Dr                          Dr   4500     (assuming $ has converted into rupees                                     

                                                                        100*45=4500)

      Foreign exchange loss        Dr     2500        (500*5=2500)

      Foreign travel advance        Cr      25,000