Answer:
Second hour
Explanation:
According to the information in the statement, we have to study not an hour, there is a grade of 70.
An extra hour, you get a grade of 80, that is, there is an increase of 10 points.
Two extra hours, you get a grade of 89, that is, there is an increase of 9 points over the previous one.
Three extra hours, a note of 92, that is, there is an increase of 3 points compared to the previous one.
Four extra hours, the grade decreases to 87. We are asked at what time the decreasing returns begin.
The diminishing return would start in the second hour because your profit is less than the previous hour, that is, you had to earn 10 or more points for the growth to be positive, which means that as of the second hour there is a decrease in the performance per hour.