Answer
$12a^{3}b^{4}$
Work Step by Step
$(-4a^{2}b^{3})(-3ab)$
$=[(-4)\times(-3)](a^{2}\times a)(b^{3}\times b)$
$=(12)(a^{3})(b^{4})$
$=12a^{3}b^{4}$
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