Explain the rule of binary addition and solve these problems

Problem $2\mathrm{.}1$:

$01010101$

$01110101$

Problem $2\mathrm{.}2$:

$01011010$

$11001010$

Problem $2\mathrm{.}3$:

$01101101$

$00010110$

Problem $2\mathrm{.}4$:

$01010110$

$11111001$

Problem $2\mathrm{.}5$:

$11010110$

$10101010$

Problem $2\mathrm{.}6$:

$01101101$

$11111001$