G7.3 and G7.4 $\quad A, B$ are positive integers less than 10 such that $21 A 104 \times 11=2 B 8016 \times 9$.
G7.3 Find $A$.
G7.4 Find $B$.
11 and 9 are relatively prime, $21 A 104$ is divisible by 9 .
$$
\begin{array}{l}
2+1+A+1+0+4=9 m \\
\Rightarrow 8+A=9 m \\
\Rightarrow A=1
\end{array}
$$
$2 B 8016$ is divisible by 11 .
$$
\begin{array}{l}
2+8+1-(B+0+6)=11 n \\
\Rightarrow 11-(B+6)=11 n \\
\Rightarrow B=5
\end{array}
$$