Divide the diagram to a square and triangle
Square = 12*12= 144m2
Triangle = 1/2 * 8*12= 48m2
Total area = 144+48=192m2
Price of weed killer needed for 1m = 19.75 divided by 100
= 0.1975
Weed killer needed for 92m2 = 0.1975*92=18.17
Weed killer needed for the whole land 19.75+18.17= £37.92