(6/4) (2/3) times the denominators (4x3=12) then times (6x3 and 4x2) add the two answer together which should be 26/12 then reverse it. 12/26 = 6/13 (I'm English so might be different for you)
The surface area of the triangular prism that will be covered with insulation is equal to the area of the two triangular faces plus the two lateral rectangular faces