Answer
$$256\ a^8b^{12}c^{16}
.$$
Work Step by Step
By raising each factor to the power and multiplying the exponents, we have
$$(-4a^2b^3c^4)^4=(-4)^4a^8b^{12}c^{16}= 256\ a^8b^{12}c^{16}
.$$
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