Rita uses 10 buttons on each rag doll she makes for her toy business. two-fifths of the buttons she uses are blue and the rest are red. if rita makes 115 rag dolls, how many red buttons does she use?

Number of rag dolls made by Rita = 115
Number of buttons Rita uses on each rag doll = 10
Then
Total number of buttons required by Rita = 115 * 10
                                                                  = 1150
Number of blue buttons used by Rita = (2/5) * 1150
                                                            = 2 * 230
                                                            = 460
Then
The total number of red buttons used by Rita = 1150 - 460
                                                                         = 690
So Rita uses 690 red buttons for making 115 rag dolls. I hope the procedure is clear enough for you to understand.

40 & 50 in the right corner are the complementary angles as when placed in a sum (added together) they make 90°