Answer:
[tex]y^6[/tex], [tex]12n^6[/tex], [tex]20x^9[/tex]
Step-by-step explanation:
When you multiply like variables with each other, you add their powers together.
So...
1. [tex](y^2)(y)(y^3)\\y^{2+1+3} \\y^6[/tex]
2. [tex](3n^2)(4n^4)\\12n^{2+4}\\12n^6[/tex]
3. [tex](5x^4)(4x^5)\\20x^{4+5}\\20x^9[/tex]
