Find the least number which must be added to $425$ to get a perfect square. Also, find the square root of the perfect square so obtained.

Find the least number which must be added to $2361$ to get a perfect square. Also, find the square root of the perfect square so obtained.

Find the least number which must be added to $8400$ to get a perfect square. Also, find the square root of the perfect square so obtained.

Find the least number which must be added to $306452$ to get a perfect square. Also, find the square root of the perfect square so obtained.

Find the least number which must be added to $566900$ to get a perfect square. Also, find the square root of the perfect square so obtained.

Find the least number which must be added to $4515600$ to get a perfect square. Also, find the square root of the perfect square so obtained.

A ladder is placed with its foot $5 \mathrm{m}$ from the bottom of a wall $12 \mathrm{m}$high. The top of the ladder just reaches the top of the wall. If the length of the ladder is $k \mathrm{m}$, find the value of $k$.