You can put this solution on YOUR website! length of the walkway = 2m.
length of the plot = 20m
width of the plot = 12m
Solution : Total width with walkway = 12 + 2 + 2 = 16m
Total length with walkway = 20 + 2 + 2 = 24m
Total area of plot and walkway = 16 * 24 sq.m ------eq.1
Total area of plot = 12 * 20 sq.m ------eq.2
Total area covered by walkway = eq.1 - eq.2 = 16*24 - 12*20 = 144 sq.m