Final answer:
The correct ratio of horses to the total number of animals on Tuesday is 16/34, as there were 16 horses and a total of 34 animals in the field.
Step-by-step explanation:
On Monday, there were 18 cows and 12 horses in the field. On Tuesday, there were 4 more horses added to the 12 already there, making a total of 16 horses. To find the ratio of horses to the total number of animals on Tuesday, we must first calculate the total number of animals. The total is the sum of cows and horses, which is 18 cows + 16 horses = 34 animals. The ratio of the number of horses to the total number of animals is therefore 16 horses to 34 animals.
The ratio can be written as 16/34. This cannot be simplified further since 16 and 34 do not share any common factors, aside from 1. Therefore, the correct answer is 16/34.