PLEASE HELP
I've tried putting all my working out into the box but it said wrong to..

£59.25

Step-by-step explanation:

It appears you can measure the height of the trapezoid [trapezium  :-)  ??].  If you can't, you can use the Pythagorean Theorem (image attached).  Draw a line from the upper right-hand corner down to the baseline--the 20m side.  You'll form a right triangle with one leg  h , hypotenuse 17m and the other leg  8m  (the difference between 20m and 12m).

(leg)^2 + (leg)^2 = (hypotenuse)^2

h^2 + 8^2 = 17^2

h^2 + 64 = 289

h^2 = 225

h = 15m

The area of the trapezium is  where the b's are the lengths of the two bases (upper and lower sides).

m^2

One can of weedkiller covers 100 m^2 of area.  You'll need 3 cans (2 cans isn't enough, and you can't buy a fraction of a can).  Tricky question!

Three cans will cost  3 x 19.75 pounds = £59.25