$$(150-100)\times 10 = 500$$. 
A shop purchased some tennis rackets at ＄$$100$$ each, and then sold them at ＄$$150$$ each. How much did the shopkeeper earn for $$10$$ rackets? 
1: ＄$$200$$ 
2: ＄$$250$$ 
3: ＄$$300$$ 
4: ＄$$500$$ 