Explanation:
B Given,
\(\mathrm{A}=\{1,2,3,4\}\)
\(\mathrm{B}=\{1,2,3,4,5,6\}\)
\(\text { Here } \mathrm{f}(3) \text { can be } 2,3,4,5,6\)
\(\text { Then, } \mathrm{f}(3)=2,(\mathrm{f}(1), \mathrm{f}(2)) \rightarrow(1,1) \rightarrow 6 \text { cases }\)
\(\mathrm{f}(3)=3,(\mathrm{f}(1), \mathrm{f}(2)) \rightarrow(1,2),(2,1)\)
\(\rightarrow 2 \times 6=12 \text { cases }\)
\(\mathrm{f}(3)=4,(\mathrm{f}(1), \mathrm{f}(2)) \rightarrow(1,3),(3,1),(2,2)\)
\(\rightarrow 3\)
\(6=18 \text { cases }\)
\(\mathrm{f}(3)=5,(\mathrm{f}(1), \mathrm{f}(2)) \rightarrow(1,4),(4,1),(2,3),(3,2)\)
\(\rightarrow 4 \times 6=24 \text { cases }\)
\(\mathrm{f}(3)=6,(\mathrm{f}(1)), \mathrm{f}(2)) \rightarrow(1,5),(5,1),(2,4),(4,2),(3,\)
\(3)\)
\(\rightarrow 5 \times 6=30 \text { cases }\)
\(\text { Total number of cases }=6+12+18+24+30=90\)Total number of cases \(=6+12+18+24+30=90\)