passport renewal - fees

[perlperl]

I am applying for passport renewal. There is US $40 fee for regular booklet.
It should be money order or certified check

If I want to get my passport back, should I send an additional $20 check ?

OR

should I enclose a self-addressed USPS Express Mail – Flat Rate Mailing Envelope only, with minimum postage of $ 18.30 ?

[perlperl]

Is it ok if I just send one single $60 check instead of sending return envelope. ??

$60 will cover both $40 passport fees and $20 for return fees.