Đáp án:
$\begin{array}{l}
A = a + 11 - a - 29\\
= \left( {a - a} \right) + 11 + \left( { - 29} \right)\\
= 0 - \left( {29 - 11} \right)\\
= - 18\\
B = a - b - 22 + 25 + b - a\\
= \left( {a - a} \right) + \left( { - b + b} \right) + 25 - 22\\
= 0 + 0 + 3\\
= 3\\
C = - a - 18 + \left( { + 18 - c + b} \right)\\
= - a - 18 + 18 + b - c\\
= - a + b - c
\end{array}$