sum of the two die is odd.
If B has occured then of necessity so has D as 7 is odd.
The even (B and D) means both events have occured, which always has the
same truth value as B, so in this case:
P(B and D)=P(B)
Alternativly draw a Venn diagam, then B is entirly enclosed withing D, and
the event (B and D) is represented by the area of overlap of B and D, which
in such a case is B.
Drawing a Venn diagram will also show why P(B or D)=P(D) when B is contained in