So lets say you sold ‘x’ number of oranges on Thursday.On Friday you sold double,therefore ‘2x’. And altogether combining the sales on Thursday and Friday you sold 108 oranges. Therefore if we add the number of oranges sold on Thursday and Friday we will get 108 oranges. The equation will be: x(number of oranges sold on Thursday) + 2x( number of oranges sold on Friday) = 108 (total number of oranges sold altogether) x + 2x = 108