Find the surface area of the prism.

The answer is:  " 52 mm² " .

Explanation:  There are a total of 5 (FIVE) sides, or "faces"; covering the surface;  

2 (TWO) triangles of equal area; and

3 (THREE) rectangles of equal area ;

The area of the rectangle given:

A = L * w = (4mm)*(3mm) = 12 mm² ;  

Multiply this by "3" ; since there are 3 (THREE) such rectangles of equal area on the surface:

     →   (12 mm²) * 3 =  36 mm² ;

Now, calculate the area of 1 (ONE) of the 2 (TWO) triangles;  both are equal in area/dimensions:

     A = (1/2) * b * h =  (1/2) * (4mm) * (4mm) = 8 mm² ;

Multiply this by "2" ; since there are 2 (TWO) such triangles of equal area on the surface;
           
           →  (8 mm²) * (2) = 16 mm² ;

Now, to find the TOTAL surface area:

We add:    36 mm²  + 16 mm²  = 52 mm² ;  →  which is our answer.