1 dollar
It is worth about $10 in good condition and about $20 in mint condition.
$20
The US did not mint a dollar coin in 1968, therefore you don't have a 1968-D silver dollar.
The U.S. didn't mint any silver dollars in the 1940s.
A typical Mint State coin is about $50.00
The Carson City Mint opend in 1869
as much as you can get for it.
It is worth around $25 in its original condition, having the original black "clamshell" case will help. This coin is made of 50% silver, meaning it has .357 of an ounce of silver.
The U.S. didn't mint any silver dollars in 1946.
There were no silver dollars issued by the US Mint in 1964.
A 1884 Silver Dollar - aka - Morgan Dollar - is worth in good condition (G4): $18; if its mint state is MS60, the value rises to: $40.
The US Mint did not issue any silver coins of any kind in 1980. If you have silver coins dated 1980, they are not US coins.