This is what I have so far.
Proof by Induction. Let $n \in \mathbb{Z}^+$ Let $P(n)$ be the statement that $10^{n+2} - 2*10^n + 7$ is divisible by 3.
($\textit{Base Case}$): Let $n = 1$. $$ 10^{1+2} - 2*10^1 + 7 = 1000 - 20 + 7 = 987 $$
$3 \mid 987$ there for $P(1)$ is true.
($\textit{Inductive Step}$): Let $k \in \mathbb{Z}^+$. Suppose $P(k)$ is true. Now we must show that $P(k+1)$ is true.
$$ 10^{(k+1) + 2} - 2*10^{k+1} + 7 $$
$$ \Rightarrow 10^{(k+2)+1} - 2*10^{k+1} + 7 $$
$$ \Rightarrow 10^{k+2}(10) - 2*10^{k}(10) - 7 $$
$$ \Rightarrow 10(10^{k+2} - 2*10^{k}) + 7 $$
I don't know how to proceed. I've tried other methods of manipulating the equation and nothing seems to work.