The part is 15 and the whole is 300. You need to find the percent.

Let n represent the percent.

Part = percentwhole

15 = n300                                 (Substitute part = 15 and whole = 300)

                         (Divide each side by 300)

                                     (Cancel common terms)

                                      (Divide: )

                        (Multiply with 100 and add percent sign)

                                          (Multiply: )

15 is 5 of 300.