Final answer:
The value of [4.2] using the floor function is 4, as it is the greatest integer less than or equal to 4.2.
Step-by-step explanation:
The student is asking for the value of the square brackets around the number 4.2. Usually, square brackets symbolize the floor function, which means taking the greatest integer less than or equal to the given number. In this case, the value of [4.2] is 4, because 4 is the largest integer that is less than or equal to 4.2. The other options provided, 5 and 0 are not correct because they are either greater than 4.2 or not the greatest integer less than or equal to 4.2, respectively.