Answer:
0000*9 = 0000
1098*9 = 9801
Step-by-step explanation:
I brute forced this...
public static void Main()
{
for (int a = 0; a <= 9; a++)
for (int b = 0; b <= 9; b++)
for (int c = 0; c <= 9; c++)
for (int d = 0; d <= 9; d++)
{
if ((9 * (a * 1000 + b * 100 + c * 10 + d)) == d * 1000 + c * 100 + b * 10 + a)
{
Console.WriteLine($"{a}{b}{c}{d}");
}
}
}