Call length L and width W. 6 ft longer than twice the width is 2W+6. Perimeter is 2L+2W=102. L=2W+6 so we substitute this in the perimeter equation: 4W+12+2W=102, so 6W+12=102, and 6W=90. Therefore W=15 and L is twice this plus 6 feet=36. Check the perimeter: 2*36+2*15=72+30=102. Checks out!