x = 1 + 2 + 3 + ... + 20 = 20*21 /2 ( Suma Gauss)
= 420 / 2 = 210
-> x = 210
y = 2 + 4 + 6 + .... + 40 = 2( 1 + 2 + 3 + .... + 20) = 2 * 210
z = 3 + 6 + 9 + ...... + 60 = 3( 1 + 2 + 3 + ... + 20 ) = 3 * 210
x + y + z = 210 + 2 * 210 + 3 * 210 = 210 * ( 1 + 2 + 3) = 210 *6 = 1260