Nathaniel can weld a railing in 75 minutes. brenda can weld a railing 25 minutes faster. how many minutes does it take them to weld the railing if they work together?

Time taken by Nathaniel  for wielding a railing = 75 minutes
Time taken by Brenda for wielding the same railing = 75 - 25 minutes
                                                                                  = 50 minutes
Time taken by both of them together
to wield the railing = (75 * 50)/(75 + 50)
                              = 3750/125
                              = 30 minutes
I hope the procedure is clear enough for you to understand. 

Here for a good time of free question