A dealer had 24 mobile phones. He sold some of them at a profit of Tk.950 each and he sold the rest at a loss of Tk.500 each....

A dealer had 24 mobile phones. He sold some of them at a profit of Tk.950 each and he sold the rest at a loss of Tk.500 each. If his total profit was Tk.9750, how many phones did he sell at a loss?