A late is stocked with 1500 trout, the # of original trout alive after x yrs is given by T(x)=1,500e^-1.4x When will there be 300 of original trout left

You might find the following useful:
http://mathonweb.com/help_ebook/html/functions_3.htm
Please let me know if you need any clarification. I'm always happy to answer your questions.

OK. In my opinion, you would be better off trying to do the problem based on the steps I showed, replacing each occurrence of 1.4 with 0.4 and recalculating, than having me do it. If you have trouble doing so, let me know.