{ d = 2u
{ 10 u + d + 36 = 10 d + u
{ d, u cifre
9 d - 9 u = 36
d = 2u
d - u = 4
2u - u = 4
u = 4
d = 2u = 8
84
x(unita') y=2x(decine) 2x*10+x-36=10*x+2x 21x-10x-2x=36 x=4 y=8 n=84
20y+y = n
n = 21y
10y+2y = 21y-36
y = 36/9 = 4
x = 2y = 8
n = 84