900 silver coin
All varieties of the 1935 British Crown have a 50% silver content.
If it was minted in or before 1935, it's 90% silver out of a total weight of 26.73 grams. If it's a circulating Eisenhower dollar from the 1970s, then it contains no silver at all.
All U.S. silver dollars from 1840 to 1935 contain the same amount of silver. They are 90% silver and 10% copper with an Actual Silver Weight (ASW) of .77344oz of pure silver.
First off, they are not sterling silver, sterling silver is 92.5% pure silver, most silver US coins are 90% silver and 10% copper, known occasionally as "coin silver". In average circulated condition, the coin is only worth its silver content, at the time of writing, it is about $5.50 in silver content. If it is in mint-state or otherwise very good condition, it might be worth more than just its silver content if you can find a collector.
If the coin is an "S" mintmarked silver proof coin, it's 90% silver.
There is no silver content in any general circulation British coin from 1947 onwards. The 10 Pence coin is made from 75% copper and 25% nickel.
90%
The silver content of the 1981 British Royal Wedding commemorative general circulation crown is zero. It is a cupro-nickel coin. No British general circulation coin has had any silver content since 1946. The 1981 silver Proof FDC Crown coin which was sold in a case, has a 92.5% silver content.
82.5% silver
None of the one dollar coins released for circulation after 1935 have any silver. So the 1935 Peace dollar was the last U.S. 90% silver one dollar coin.
You possess a Peace Dollar - a 1935 coin in very fine condition (VF20) is worth: $25.00.
No S.B.A. coin was struck in silver, so the silver content is zero. All are copper-nickel.