Under a Gold Standard in Which One Dollar Could Be

Under a gold standard in which one dollar could be turned in to the U.S.Treasury and exchanged for 1/20th of an ounce of gold and one German mark could be exchanged for 1/100th of an ounce of gold,an exchange rate of ________ marks to the dollar would stimulate a flow of gold from the United States to Germany.

A) 7
B) 6
C) 5
D) 4