Herman and his workout partner are lifting weights together, doing many sets of each exercise. On a certain exercise, Herman is using a 15-kilogram bar, increasing the amount of weight he lifts by 4 kilograms on each set. His partner, meanwhile, started out using a 17-kilogram bar and is upping the weight by adding 2 kilograms on every set. Eventually, Herman and his workout partner will be lifting the same amount, and will take turns using the same barbell. How many sets will they have completed? How much weight will they be lifting then?