Azim sold 5kg chocolates boxes for 'c' taka per box, and Dobir sold 3kg chocolates boxes for 'c' taka per box. Azim increased the price per box by 'd' taka and Dobir decreased the price per box by 'd' taka, and afterwards, the two shops were selling chocolates for the same price per kg. In terms of 'd', what was the original price of Azim's 5 kg chocolate box?