Ben purchased 1000 stocks of Appen on 12th September at the price of $3.80 per share using the margin trading facility offered by his broker. The broker requires 50% initial margin and 40% maintenance margin. There are no transaction fees and the broker charges no interest or fees for the margin trading facility. On 14th September, Ben sells the Appen stocks he purchased at the price of $3.6 per share.

Calculate the rate of return he earned as a percentage of his initial investment.