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For Q1, I changed R to "dR/dt" because it concerns the rate of water flowing out over time. Integrating this with the bounds being 0 and 3 gives you the total volume of water released when 0 < t < 3. For Q1 ii), if you let dR/dt = 0 and then solve for t, you get t=7 or t=-1, but time cannot be negative, so t=7 is the only correct answer.

For Q2, it's just a simple matter of integrating dh/dt and using the given information (when t=4, h=2) to find the constant C. Then you can find the height of a 12 year old plant by subbing in t=12.

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