The soviet union, great britain, the united states, and france signed a peace treaty in 1955 with?

Japan signed the Treaty of San Francisco on 8 September 1951. 

Austria, occupied after the war because it had been a part of Germany during World War II, signed the Austrian State Treaty on 15 May 1955, in Vienna, with the USSR, USA, Great Britain, and France. The four powers withdrew from Austria, which was not punished for the war since Hitler forcibly annexed it, but they were required to stay neutral and not join NATO or the Warsaw Pact. 

Germany, because it was divided after the war, couldn't sign a formal peace treaty, and the West and the postwar Soviet bloc never did agree on a framework for doing so. The Western Allies announced in 1951 that their state of war with Germany was officially over for purposes of international law, and the USSR did the same early in 1955. Finally, on 12 September 1990, with German reunification about to happen, the Treaty on the Final Settlement with Respect to Germany was signed in Moscow between East and West Germany and the USSR, Great Britain, USA, and France, in which those four powers formally renounced all rights they had in their sectors of Germany, and gave their blessing to German reunification, which took place on 3 October 1990.

It was signed with the Austrian Government which re established Austria as a sovereign state.

Use the formula: (n-2)×180, where n is the number of sides(18-2)×180= 28800, now this is the full exterior angle of 18-gon so you divide it by 18.28800÷18=160