In this problem, surface area is the sum of the area of the base triangle and
the areas of three lateral triangle.


The area of any triangle is half the product of the length of its base (= some side) and the length 
of the altitude drawn to this side

    area = .


For the base triangle, you are given b= 30 mm, h= 20 mm, so its area is  

     = 30*10 = 300 mm^2.


For three lateral triangles, their areas are equal (since the triangles are congruent).


Using the same rule, you find the area of each triangle  = 30*13 = 390 mm^2.


So, the total surface area is

    300 + 3*390 = 1470 mm^2.


It is the answer to your question.