a) 11111111 – 2222 = 1111. 1000 + 1111 – 1111.2 = 1111. (1000 + 1 – 2)
= 1111 . 9999 = 1111 . 3 . 3333 = 3333 . 3333
b) \begin{align}
& \underbrace{111...1}_{2n}-\underbrace{222...2}_{n}=\underbrace{111...1}_{n}.\left( 1\underbrace{000...0}_{n}+1 \right)-\underbrace{111...1}_{n}.2 \\
& =\underbrace{111...1}_{n}.\left( 1\underbrace{000...0}_{n}+1-2 \right)=\underbrace{111...1}_{n}.\underbrace{999...9}_{n}=\underbrace{333...3}_{n}.\underbrace{333...3}_{n} \\
\end{align}