If by "long leg lengths" you mean the hypotenuse then the area is 116 sq. units. If you mean the bases of the triangles then the area is 170 sq. units.
If the length of 12 is the hypotenuse, we first must find the base of the triangles using the Pythagorean theorem:
This means we have two triangles and a rectangle. The area of the rectangle is 5(10) = 50 sq. units. The area of each triangle is 1/2(6.6)(10) = 33. Adding all 3 together we have:
50+33+33 = 116 sq. units.
If the 12 is the base, then we have the rectangle with the area of 5(10) = 50 and two triangles each with an area of 1/2(12)(10) = 60:
The answer would be £20, you would turn this into a proportion and doing that you'd have 70/100=14/x(x being the full cost) then you cross multiply and doing so you get 1400=70x and 1400 divided by 70 equals 20, so your answer is £20