Please show the formula

Assume that a Big Mac hamburger is selling for 1.99 in the United Kingdom, the same hamburger is selling for $2.71 in the United States, and the actual exchange rate (to buy 1.00 with dollars) is 1.30. According to the British pound is against the US dollar. a interest-rate parity; overvalued b. purchasing-power parity; overvalued c. purchasing-power parity; undervalued d. interest-rate parity; undervalued