Population Genetics - Calculating Mean Fitness (Hardy Weinberg)

NOTE: After speaking with my professor, it turns out that this is actually not a question we have covered in class, and she just forgot to tell us to skip it!!  If you want to answer it, that is fine, but it is not pertinent.

QUESTION:
I don't know if I am just going cross eyed from studying too much or what, but I cannot for the life of me figure out how to simplify this equation!  Here is the question:

What is the mean fitness in the population for the following genotypes and their fitnesses?  Simplify (Remember p^2 + 2pq + q^2 = 1)

Initial Zygote Frequency AA = p^2
Initial Zygote Frequency Aa = 2pq
Initial Zygote Frequency aa = q^2
Fitness AA = 1+t
Fitness Aa = 1
Fitness aa = 1+s

The answer is supposed to be 1 + tp^2 + sq^2 but I am not sure how to simplify down into that answer.