Instead of mailing a check,  you may also send the payment electronically to save the hassels.

Make sure that you deliver the agreed amount to <etf@MathEnglish.com> (PayPal) by using the Friend Option as below to avoid extra charge.
See this sample video here.

Or, you will have to pay for the transaction cost about 3%.

Please leave a note with the Order ID or the email conversation for tracking purpose.