Okay so CBE is a right angle which equals 90 degrees. CBD and DBE makes up CBE which is 23 degrees is part of CBD. So subtract CBE from CBD to get DBE which is 67 degrees.
This just wants the derivative which you can solve for.
You can do this using a negative expononet or using ...the rational rule forget its name*.... you shoudl get 9000/(t+12)^2
*Quotient rule
<span>Can a Segment have more than one bisector. Yes A segment can have more than one bisector. For every line segment, there is one perpendicular bisector that passes through the midpoint. There are infinitely many bisectors, but only one perpendicular bisector for any segment.</span>
I'm sorry but your photo doesn't really show the whole paragraph clearly so I can't answer
