[tex]3w^{4} (-5w^{2} ) = -15w^{6}[/tex]
I think this is what you want? When multiplying with exponents, you either add or multiply the exponents.
When you multiply the exponent:
(x²)³ = [tex]x^{6}[/tex]
[tex](3x^{4} )^{2}[/tex] = 9[tex]x^{8}[/tex]
When you add the exponents:
(x²)(x³) = [tex]x^{5}[/tex]
(x²)(x²) = [tex]x^{4}[/tex]
[tex](x^{4} )(x^{3} ) = x^{7}[/tex]
