Originally Posted by

**Ackbeet** Plugging in the value of $\displaystyle t$ and solving for $\displaystyle x$ at the appropriate time was what was required. A simple step that you've already done in your head, no doubt; however, in order to show it, you just need to write it down.

As to the integral, it's a situation with an unclear notation. The correct $\displaystyle t$ integration is $\displaystyle k(5t-\frac{1}{2}\,t^{2})+C$, not

$\displaystyle 5kt - \frac{1}{2}t^{2} + C$. See the difference?

As for part b), try finding out what her sales rate is at the given time.