Aparticular english class has 40 students. as the students leave the room, only 28 students are left after three seconds. what is the rate of change of the number of students in the classroom each second?

Student who gone from class within 3 sec = 12

within 1 sec, it would be 12/3 = 4

So, your answer is 4

it is a. 4.2 because 7.6-3.4 gets the remaining length of 4.2. i might be wrong but i am pretty sure this is the answer.