Calculate CDEFtrapezium

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You need to find the length of A F and BC first

Lets call BC --> 'x'

Lets form an equation

9 + 9 + x + x = 28

18 + 2x = 28

- 18

2x = 10

/ 2

x = 5

So now we have the length BC

We can subtract this length from the 11cm to find the vertical height of the trapezium

11 - 5 = 6

Now we have all we need to work it out.

area = (a + b) / 2 x h

area = (5 + 9) / 2 x 6

area = 42 cm^2

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answer:   b

step-by-step explanation:

x2 = 16

x can not be a negative number because 16 is positive

the only answer would be positive 8