#27 Perimeter of a rectangle
#39 Perimeter of regular pentagons
#64 Area of a rectangle, but first solve for x
#69 Area of a triangle
#95 Calculating radius when given area of a circle
#128 Area of a triangle
#129 Tricky perimeter of a semi circle
#226 Area of the space between two circles
#255 Pythagoras and area of a trapezium
#256 Using circumference to calculate area
#257 Doubling the length of a rectangle to see how area changes