The part is 30 and the whole is 90. You need to find the percent.

Let n represent the percent.

Part = percentwhole

30 = n90                                 (Substitute part = 30 and whole = 90)

                            (Divide each side by 90)

                                     (Cancel common terms)

                                (Divide: )

                   (Multiply with 100 and add percent sign)

                                (Multiply: )

30 is 33.33 of 90.