Step 1. Gather like terms
[tex]13*3 x^{2} xy^{3} y^{5}[/tex]
Step 2. Use product rule: [tex] x^{a} x^{b} = x^{a+b} [/tex]
[tex]13*3 x^{2+1} y^{3+5}[/tex]
Step 3. Simplify [tex]2+1[/tex] to [tex]3[/tex]
[tex]13*3 x^{3} y^{3+5} [/tex]
Step 4. Simplify [tex]3+5[/tex] to [tex]8[/tex]
[tex]13*3 x^{3} y^{8} [/tex]
Step 5. Simplify
[tex]39 x^{3} y^{8} [/tex]
Done!
