Answer:
200
Step-by-step explanation:
Given the first term 39 and the last term 11 then the sum of the 8 layers can be calculated as
[tex]S_{n}[/tex] = [tex]\frac{n}{2}[/tex] ( f + l) ← f is the bottom layer anf f the top layer, thus
[tex]S_{8}[/tex] = [tex]\frac{8}{2}[/tex] (39 + 11) = 4 × 50 = 200
