Let x be the number of English papers to grade and y be the number of math tests to grade.
The time it takes to grade x English papers is 1/4x hours.
The time it takes to grade y math tests is 1/6y hours.
The teacher wants to spend over 3 hours but under 6 hours grading, so the inequalities are:
1/4x + 1/6y >= 3 (minimum number of hours)
1/4x + 1/6y <= 6 (maximum number of hours)
The graph of the system of inequalities would look like this:
The minimum number of hours line: 1/4x + 1/6y = 3 (solid line)
The maximum number of hours line: 1/4x + 1/6y = 6 (solid line)
The shaded region between the two lines represents the range of hours the teacher wants to spend grading.