Simplify. Your answer should contain only positive exponents.
1) 2m² * 2m³
2) m⁴ * 2m⁻³
3) 4r⁻³ * 2r²
4) 4n⁴ * 2n⁻³
5) 2k⁴ * 4k
6) 2x³y⁻³ * 2x⁻¹y³