Let $R$ be a relation from the set ${1,2,3,\dots,60}$ to itself such that R={(a,b):b=pq,    where p,q≥3 are prime numbers}.R = \{(a,b) : b = pq, \;\; \text{where $p,q \geq 3$ are prime numbers} \}.R={(a,b):b=pq,where p,q≥3 are prime numbers}. Then, the number of elements in $R$ is :