A firm compares two alternative ways of acquiring customers. Advertising on Google Ads costs $500 per month and it generates 1000 extra visits to the firm's website, 100 of which result in a purchase. On the other hand, advertising on Ask.com costs $250 per month and it generates 400 extra visits to the firm's website, 20 of which result in a purchase. The sales from Google Ads are, on average, 10% higher than sales from visitors from Ask.com. 

Compute the amount of sales per dollar spent on advertising for Google Ads and Ask.com, respectively. 

Compute the advertising cost per sale for Google Ads and Ask.com, respectively.