Sixth graders have an average of 60 minutes of homework, four days a week. l seventh graders have 20 minutes more per day than sixth graders. how many minutes per week of homework does a seventh grader have?

I'm assuming this means that 6th grade has 60 minutes per day.
60+20=80
80 x 4 = 320
320 minutes of homework 

If it means that 6th grade has 60 minutes in total for the four days, then:
60/4=15
15+20=35
35 x 4 = 140
140 minutes of homework

Hope I helped!