Hi! Please help. I will go to class in a few minutes. I don't have an equation for it. Thanks!!!

A merchant has 3 items on sale: namely, a radio for $50, a clock for $30, and a flashlight for $1. At the end of the day, she has sold a total of 100 of the 3 items and has taken exactly $1000 on the total sales. How many radios did he sell?