The base of a rectangle is a length and does not have any area. Therefore, the area can not be calculated.
Area = 0.5*base*altitude
The base of a cone is a circle. The area of a circle is found by multiplying the diameter by Pi.
Area in square units = base*height
bigger base + smaller base x height/2
area of a square is base times height area of a triangle is base times height divided by two!!
base X height
Area = 1/2*base*perpendicular height.
0.5*base*perpendicular height, in appropraite units for area.
Area = 1/2*base*perpendicular height
Given only the information in the question, there is no option but to measure the pentagon at the base and calculate its area.
You will need to know the height before you can calculate the base form the area.