A problem on the review set

You have been asked to design a soccer field. Unlike a football field, whose dimensions cannot vary, a rectangular soccer field may have a width between 50 to 100 yards and a length between 50 to 100 yards. Your soccer field must meet certain specifications. The Perimeter of the field must be 320 yards and length must be 40 yards more than its width. Each square yard of turf will cost you $3/yd^2 and your budget cannot exceed $20,000 for turf. What are the dimension of the field?

please help me asap cuz my test is tomorrow

thanks in advance