Originally Posted by

**22upon7** Hi,

I'm working on my application task exercises for Trigonometric graphs, but I can't seem to work this sum out, A step by step explanation would be great:

**The depth, ****$\displaystyle D(t)$*** metres, of water at the entrance to a harbour at t hours after midnight on a particular day is given by *$\displaystyle D(t) = 10 + 3 sin (\frac{\pi t}{6}), 0 \leq t \leq 24$

**1. Find the value of $\displaystyle t$ for which $\displaystyle D(t) \geq 8.5$**

Any help would be greatly appreciated,

Thanks,

Dru