A TV transmission tower antenna is at a height of $20 \mathrm{m}$. How much service area can it cover if the receiving antenna is $\left(\mathrm{i}\right)$ at ground level, $\left(\mathrm{ii}\right)$ at a height of $25 \mathrm{m}$? Calculate the percentage increase in area covered in case $\left(\mathrm{ii}\right)$ relative to case $\left(\mathrm{i}\right)$.