Respuesta :
1 - 9 -> 1 cifra => 9 * 1 (9 = 9-1+1)
10 - 99 -> 2 cifras => 90 * 2 (90 = 99 - 10 +1)
100 - x -> 3 cifras => (x - 100 + 1) * 3
9 + 180 + 3 ( x - 99 )=207
3 (x - 99) = 18
x - 99 = 6
x = 105
10 - 99 -> 2 cifras => 90 * 2 (90 = 99 - 10 +1)
100 - x -> 3 cifras => (x - 100 + 1) * 3
9 + 180 + 3 ( x - 99 )=207
3 (x - 99) = 18
x - 99 = 6
x = 105