How many justices must agree to an opinion for the supreme court to issue a decision
a) all of the nine justices
b) seven of the nine justices
c) six of the nine justices
d) five of the nine justices

Ok so, at least Six justices have to vote at all to decide an issue, and no matter how many justices are voting, a Majority Vote must be attained. So if Nine justices were to vote, Five justices would have to be for one side, as five would be majority over the four remaining justices.