We have to assume that the pentagon shape is regular so that all sides have equal length. The lateral area is the sum of the areas of 5 triangles, all with the same base length and height.
.. lateral area = 5*(1/2)*(3 cm)*(9 cm) = 67.5 cm^2
.. base area = given as 15.5 cm^2
Total area = lateral area +base area = (67.5 +15.5) cm^2 = 83 cm^2.
