a)

$0,\left(3\right)+0,\left(5\right)=0,333\dots +0,555\dots =0,888..=0,\left(8\right)$

b)

$0,\left(12\right)+0,\left(45\right)=0,121212\dots +0,454545\dots =0,575757\dots =0,\left(57\right)$

c)

$0,\left(127\right)+0,\left(13\right)=0,127127127127\dots +0,131313131313=0,258440258440\dots =0,\left(258440\right)$