If S = {y : y = x^3, x is a negative integer}, then _____ belongs to S.
Each set X, contains 5 elements and each set Y, contains 2 elements and ⋃20r=2Xr=S=⋃nr=1Yr. If each element of S belongs to exactly 10 of the X′sr and to exactly 4 of Y′sr then find the value of n.