How many rectangles of different sizes and quantities can you fit in one area?

Example: Given an area that is 800 units wide by 600 units long, can you fit one 500 x 200 rectangle, one 250 x 200 rectangle, and twenty 50 x 50 rectangles? If so, how much space is left. If not, which rectangles will not fit?

Usage:

1. Enter a width and height in the Size of Area field.
2.Enter some widths and heights and, optionally, quantities in the Blocks
3.Hit the enter key in any field to run the program