Final answer:
There are a total of 1296 functions.
Step-by-step explanation:
To find the total number of functions, we need to consider that each input value in the domain has 6 possible output values in the codomain. Therefore, for each input value, there are 6 choices. Since there are 4 input values, we multiply the number of choices for each input value: 6 x 6 x 6 x 6 = 1296. Therefore, there are a total of 1296 functions.