A merchant imported a batch of 80 porcelain vases for $4,800. Upon receiving the batch, he found 5 vases to be broken and threw them away. He sold 4/5 of the remaining vases at a profit of 40% and the rest at a loss of 10% on his cost price based on the 80 vases. Find his overall profit or loss as a percentage of his cost price based on the 80 vases.