Question 420163
This is an arithmetic sequence with the following parameters:
n = 10 (the number of layers)
{{{a[10] = 4}}} (the number of blocks in the topmost layer)
d = -10 (the next higher layer has 10 fewer blocks)

Now {{{a[10] = a[1] + (n-1)d}}} ==> {{{4 = a[1] + 9*-10}}} ==> {{{a[1] = 94}}}.

==> {{{S = (n/2)*(a[1] + a[n]) = (10/2)(94 + 4) = 490}}}.