Answer: a) prefer buying in the US
Explanation: at an exchange rate of 1 peso = 0.771$
Buying in the US will cost him 500$, whereas buying it in Mexico will cost him 8188 pesos which will be equivalent to 8188 x 0.771$ = 6312$
Ignoring any other costs like import, tax etc. John will definitely prefer buying his lawn mower in the US.