$[20$ Points$]$ Suppose that $x=(x_1,$dots,$x_n)$ and $x^{\text{'}}=(x_1^{\text{'}},$dots,$x_n^{\text{'}})$ are two sequences of $n$ plaintext blocks. Let's suppose $x$ and $x^{\text{'}}$ are encrypted in OFB mode using the same key and the same IV$.$ Show mathematically $($with explanation$)$ how an adversary can compute

$xo+x^{\text{'}}.$ Under what conditions in CBC mode can an adversary also potentially compute

$x_{i}o+x_j$ utilizing just the ciphertext they see? State this condition and show it mathematically

$($with explanation$).$