Answer: 296
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Explanation:
You'll need the chain rule for this one.
[tex]y = 3x^3 + 4x\\\\\frac{d}{dt}(y) = \frac{d}{dt}\left(3x^3 + 4x\right)\\\\\frac{dy}{dt} = \frac{d}{dt}\left(3x^3\right) + \frac{d}{dt}\left(4x\right)\\\\\frac{dy}{dt} = 3\frac{d}{dt}\left(x^3\right) + 4\frac{d}{dt}\left(x\right)\\\\\frac{dy}{dt} = 3*3\left(x^2\right)*\frac{dx}{dt} + 4\frac{dx}{dt}\\\\\frac{dy}{dt} = 9x^2\frac{dx}{dt} + 4\frac{dx}{dt}\\\\\frac{dy}{dt} = (9x^2+4)\frac{dx}{dt}\\\\[/tex]
Now apply substitution
[tex]\frac{dy}{dt} = (9x^2+4)\frac{dx}{dt}\\\\\frac{dy}{dt} = (9*4^2+4)*2\\\\\frac{dy}{dt} = 296\\\\[/tex]
