30.5. Let each of the characters $A, B, C, D, E$ denote a single digit, and $A B C D E 4$ and $4 A B C D E$ represent six-digit numbers. If
$$
4 \times A B C D E 4=4 A B C D E,
$$
what is $C$ ?
30.5. 2
Let $x=A B C D E$. Then $4 \times A B C D E 4=4 A B C D E$ implies
$$
4(10 x+4)=400000+x,
$$
which gives us $x=10256$, so that $C=2$.