What do I do with the E(t) term in this differential equation?

[GottaLoveMath]

Homework Statement

Please see the attached file.

Homework Equations

The Attempt at a Solution

If my math is right so far, I am basically stuck as to what to do with the E(t) term. [/B]

 

[RUber]

It looks like this is a function of t, so E(t) = t.

 

[RUber]

The rest all looks right to me.
By the way, normally just posting an attachment is frowned upon. Especially one that won't open using the forum's built-in viewer options.