How do I maximize a function?

[killersanta]

Homework Statement

http://img262.imageshack.us/img262/678/im000724.jpg

Uploaded with ImageShack.us

The Attempt at a Solution

http://img843.imageshack.us/img843/5651/im000726.jpg

Uploaded with ImageShack.us

I got all the way to g, but I don't know how to maximize a function.

 

[killersanta]

I think I set y(t) to 0. If this is the case, I get:
0 = -100e^(-1/20t) + 150e^(-1/40t)

How do I get rid of the e's? I'm not sure how with the numbers is front. Without the numbers in front I know I could rise them to ln.

 

[killersanta]

Nevermind, I got it...56.25lbs...

 

[Coto]

Hey killersanta.. it seems like this is probably what you've done, but you should have set y'(t) to 0, not y(t). Considering you get an answer which seems reasonable and is not 0, it seems like you've self-corrected already.. but just to be sure.

 

[killersanta]

Yeah, I caught that. Thank you though.