The current area is 12x4 which is 48yards^2. 60 percent of that is 48x0.4=19.2. Now you can just put some random numbers that when multiplied = 19.2. For ex. 2 and 9.6, 4 and 4.8.
If you add the percentages that visit each mall, (62% +73%), you count twice those that visit both malls. Subtracting that percentage (48%) from the sum (135%), you get the percentage that visit either mall ... 87%.
