History of Space Exploration: Chapter 5, Exercise 3 — Possible Solution
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THE FIGURES
$25.4 billion in 1973 dollars (about $257 billion in 2020 dollars), and $25
billion (about $187 billion in 2024 dollars).

HOW TO DECIDE
Quote the original-period figure and name its year, and give a modern
conversion only with its method. Check which costs each figure includes, the
price index used, and the source of each number. The chapter does not explain
why the conversions differ.