If the wall with 4 ft. of storage area can fit 6 sections of plant and the wall with 7 ft. Can fit 5, that means each section is 3 ft. because 7-4=3, so that extra section on the wall with 4 ft. You do this because there is one extra section on the wall with four. Knowing this, the wall with 7 ft. Would be the 7 ft. + 5 sections of 3 ft. So 7+(5x3) = 22. On the wall with 4 ft., do the same,
4+(6x3) =22. Since they are equal and the walls are supposed to be equal, we can confirm this is the right answer