I cannot Understand the marked lines
The lines in blue in your image pretty well explain what is happening in the pseudocode. Are you having trouble understanding the problem description?
No I understand the description. But I don't understand the form of writing the code . Why in the first line he wrote units -500 and why in the second line he wrote units - 1000
"every unit in excess of 1000" is (units - 1000)
So the code is a direct translation of the description above.
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