#### Answer

$-24x^7y^4$

#### Work Step by Step

RECALL:
(i) $a^m \cdot a^n = a^{m+n}$
(ii) $(ab)^{m} = a^mb^m$
(iii) $(a^m)^n=a^{mn}$
Use rule (ii) above to obtain:
$=(-3xy^4) (2^3)(x^2)^3
\\=(-3xy^4)(8)(x^2)^3$
Use rule (iii) above to obtain:
$=(-3xy^4)(8x^{2(3)})
\\=(-3xy^4)(8x^6)$
Multiply the numerical coefficients, then use rule (ii) above to obtain:
$=-24x^{1+6}y^4
\\=-24x^7y^4$