chapter 6 assignment please provide a clear explanation also and calculations

Assume that in year 1 an economy produces 10,000 units of output and they sell for $100 a unit, on average. In year 2, the economy produces the same 10,000 units of output, and sells it for $50 a unit, on average. What happened to the to nominal GDP and to real GDP between years 1 and 2? Why? Provide calculations of both nominal and real GDP for years 1 and 2