David lives in Canada. He operates a pizza business in his native town. Robert is Canadian, but he works in the United States. On a typical day, David makes $275 in sales, of which he pays to the government $25 in sales taxes. Robert makes $150 in wages, of which he pays the US government $15 in income taxes. There are no other costs or taxes. Based on this information, compute David and Robert's contribution to the following measures of income:
a. Canadian GDP
b. Canadian GNP
c. US GDP
d. US GNP