Step 1: Identify vowels and consonants in RESIDE.
RESIDE contains:
R (consonant), E (vowel), S (consonant), I (vowel), D (consonant), E (vowel)
Step 2: Apply transformation rules.
Vowel → previous letter
Consonant → next letter
Transforming:
\[
\begin{aligned}
R &\rightarrow S \\
E &\rightarrow D \\
S &\rightarrow T \\
I &\rightarrow H \\
D &\rightarrow E \\
E &\rightarrow D \\
\end{aligned}
\]
So the new word is: S D T H E D
Step 3: Find third letter from the right.
From the right: D (1st), E (2nd), H (3rd)