Finding Area varies based on what you are trying to find.
Area of a triangle is 1/2(Base)(Height)
EX: B=10 , H= 15
A=1/2(10)(15)
A=5(15)
A=75^2
Area of a Square or rectangle is Length(Width)
EX: L=10 , W=15
A=10X15
A=150^2
Area of a circle is 3.14(Radius^2) or 3.14(Diameter)
R=10 , D=20
A= 3.14(10^2)
A=314
OR
A=3.14(20^2)
A=1256