la primera serÃa:
[tex] \times + \times + 1 = 157[/tex]
2X. = 157-1
X. = 156/2
X. =. 78
la tercera serÃa:
X + 2x+ 4x+8x = 90
15x = 90
90/15
6
6 + 12 + 24+ 48 = 90
