Check the date and post new question, no Quarter Eagles were struck in 1813.
mint mark is to the left of the value on the reverse.
The mint mark on a $5 gold coin from that era is on the reverse (tails) side, just below the eagle.
On the reverse just to the left of the arrows
depending on condition, about $300
The P is the mint mark for Philadelphia.
The mint mark for the 1909 Half Eagle is located on the reverse {eagle} side of the coin just to the left of the arrow points.
A date is needed. Post new question.
Please post a new question with the coin's date and mint mark.
Assuming the coin is circulated and no mint mark retail values are $312.00-$420.00
From about $1300 to $75,000 depending upon the mint mark and the condition of the coin.
With an "S" mint mark on the reverse, about $1,000 for its gold content. With no mint mark, $6,000 or more. But any such coin should be inspected by a professional to ensure that it's not counterfeit or altered.
The mint mark on $20 gold coins minted from 1849 to early 1907 is located on the reverse [tails] side of the coin just beneath the eagle. The mint mark for the Saint-Gaudens $20 gold coin minted from late 1907 to 1933 is located on the obverse [heads] side of the coin just above the date.