The Mistake Fragment

Find the algebra mistake:

(Roll the mouse over the algebra to see a hint in red)

The Correction

(Roll the mouse over the area above to see the correction in blue)

An Explanation

There is no way to combine the sum of two exponentials with a common base (the exponents add when two exponentials with a common base are multiplied together). The only option here is to factor out either e^-6 (preferably) or e^-2, as follows: