Let me just give you a hint:
The formula for finding the area of a trapezoid is
Area equals 1/2 times hieght, times the product of base 1 and base 2.
I hope that was enough to help you.
Good Luck! ;)
Let me give you some further hints:
Step 1) Use Heron's formula to find the area of triangle(DBC).
Heron's formula: Area = sqrt( s · (s - a) · (s - b) · (s - c) )
where a, b, and c are the sides of the triangle: e.g., a = 8, b = 7, and c = 9
and s is the semi-perimeter: s = (a + b + c) / 2
Step 2) Draw BP perpendicular to DC with P on DC.
This makes BP the height of triangle(DBC).
Find the value of BP by using the formula for the area of a triangle: A = ½·base·height
You know the area from Step 1, let the base be 8, and find the value of the height.
Step 3) Look at triangle(BPC).
You know the value of BC and, from step 2, you know the value of BP.
Use the Pythagorean Theorem to find the value of PC.
Step 4) Draw AQ perpendicular to DC with Q on DC.
DQ = PC; so you know the value of DQ since you found the value of PC in Step 3.
AB = DC - DQ - PC.
Step 5) Now use the formula to find the area of a trapezoid; you now have all the parts.