Work Step by Step
Given: $E(t)=-10t^3+140t^2-20t+18150$ Since $E(t)=20300$, we obtain: $-10t^3+140t^2-20t+18150=20300$ Subtract $20300$ from both sides: $-10t^3+140t^2-20t-2150=0\\ \rightarrow t^3-14t^2+2t+215=0$
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