## College Algebra (6th Edition)

$=18x^{9}y^{5}$
When multiplying two exponential expressions, group factors with the same base: $$(-9x^{3}y)(-2x^{6}y^{4})$$ $$=(-9\times(-2))(x^{3}\times x^{6})(y\times y^{4})$$ $$=18x^{(3+6)}y^{(1+4)}$$ $$=18x^{9}y^{5}$$