Multiples of 3 or 4

Difficulty: Medium · Topics: Discrete Mathematics, Sets, Venn Diagrams

A=\xmid 20≤ x≤ 80,\ x=3n,\ n∈mathbbN\

B=\xmid 50≤ x≤ 123,\ x=4n,\ n∈mathbbN\

How many elements does Acup B have?