Chapter 1 - Equations and Inequalities - 1.2 Applications and Modeling with Linear Equations - 1.2 Exercises - Page 104: 43

(a) $14,000x$ (b) $1.9\ hr$

(a) In $x$ hours with $100\ ft^2$ of new plywood, we have $F=140\mu g/hr/ft^2\times x\ hr\times100ft^2=14,000x\ \mu g$ (b) The concentration can be found as $\frac{F}{800}$. To reach $33\mu g/ft^3$, we have $\frac{F}{800}=33$ or $14,000x=33\times 800$ which gives $x\approx1.9\ hr$