Anyone knows how to do this?

can’t find !

Hi, can anyone show me how to do this problem? 100 points for this. in advance

Find the sum of the given arithmetic series. 24 + 17 + 10 + 3 + + (–39)

Abarge can safely haul no more than 400 tons across the river. the barge has an empty weight of 24 tons. the average weight of the railroad cars is 4 tons each.bhow many railroad cars can the barge haul?