The area of a trapezium is a= 1/2 h (a+b) where h is the height and a and b are the lengths of the trapezium. find the area of the trapezium with the following measurements :
h= 2.0 mm, a= 7.5 mm, b= 10.8 mm
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So assuming you meant to type a=7.5mm and b=10.8 (uppercase and lowercase letters matter) then

pemdas
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exponents
mulitplication or division
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area=1/2 times h times (a+b)
area=1/2 times 2 times (7.5 +10.8)
area=1/2 times 2 times (18.3)
area=1 times (18.3)
area=18.3 square mm also written as 18.3 mm^2

area=18.3 square mm or 18.3mm^2