please can you help me with this problem
(a) Note: $\displaystyle 10 \equiv 0 \ (\text{mod } 10)$
So we have:
$\displaystyle \begin{aligned}n & \equiv d_0 + d_1{\color{red}10} + d_2{\color{red}10}^2 + \cdots + d_{k-1}{\color{red}10}^{k-1} + d_k{\color{red}10}^k \\ & \equiv d_0 + d_1({\color{red}0}) + d_2({\color{red}0})^2 + \cdots + d_{k-1}({\color{red}0})^{k-1} + d_k({\color{red}0})^k \quad (\text{mod } 10) \\ & \ \ \vdots\end{aligned}$
Use the same method for (b)