Question

B={df,g)

Answer 1

We have two sets of letters $B=\{d,f,g\}$ and $G=\{a,d,h\}$.

Intersection of sets $B$ and $G$ is set $I$ that contains elements that are common to $B$ and $G$, mathematically

$I=\{x:x\in B\wedge x\in G\}$

Or simply $I=B\cap G=\{d\}$.

Union if sets $B$ and $G$ is set $U$ that contains elements from $B$ or $G$ thus

$U=\{x:x\in B\vee x\in G\}$

Or again simply $U=B\cup G=\{d,f,g,a,h\}$.

Hope this helps.