Answers:
Total Area = 342.5 square meters
Total Cost = 138 pounds
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Work Shown:
Break the figure up as shown by the dashed lines. Think of cutting along those lines to form 3 separate figures. The trapezoid on the left has area
A = h*(b1+b2)/2
A = 5*(11+12)/2
A = 57.5
The rectangle in the middle has area
A = L*W
A = 12*15
A = 180
The trapezoid on the right has area
A = h*(b1+b2)/2
A = 10*(12+9)/2
A = 105
Overall, the entire figure has area of 57.5+180+105 = 342.5 square meters
1 can costs £6 and it covers 15 square meters. We need to cover 342.5 square meters
342.5/15 = 22.8333333333333 approximately
Round up to the nearest whole number to get 23
We need 23 cans to be able to paint 342.5 square meters or more
Note that 22 cans won't be enough because 22*15 = 330 is short of 342.5
While 23 cans is more than enough since 23*15 = 345. It's better to have leftovers than come up short.
Since each can costs £6 and we need 23 of them, the total cost would then come to 6*23 = 138 pounds