Let \( A=\{1,3,4,6,9\} \) and \( B=\{2,4,5,8,10\} \). Let \( R \) be a relation defined on \( A\times B \) such that \( R=\{((a_1,b_1),(a_2,b_2)):\; a_1\le b_2 \;\&\; b_1\le a_2\} \). Then the number of elements in the set \( R \) is:
\( 26 \)
\( 160 \)
\( 180 \)
\( 52 \)
