Read this and answer the question. If the question is unanswerable, say "unanswerable".

After Nasser died in November 1970, his successor, Anwar Sadat, suggested that rather than a unified state, they create a political federation, implemented in April 1971; in doing so, Egypt, Syria and Sudan got large grants of Libyan oil money. In February 1972, Gaddafi and Sadat signed an unofficial charter of merger, but it was never implemented as relations broke down the following year. Sadat became increasingly wary of Libya's radical direction, and the September 1973 deadline for implementing the Federation passed by with no action taken.

In what year was the merger charter signed?
1972