Me with balloon mortgages?

1. a bank is advertising the following mortgage: $245,000
20/4 balloon
5.8% annual rate

monthly payment: $1,727.11
balloon payment: $216,789.79

what is the total cost of this balloon mortgage?

I just answered this question. Here's my answer.

Home price is $245,000. There is no down payment mentioned. 
I understand 20/4 as amortized over 20 years and balloon payment after 4 years.

Total cost would be =  Balloon payment + Total monthly payment 

4 years x 12 months = 48 months
Balloon payment =       216,789.79 x 1 mo =   216,789.79
Total monthly payment = 1,727.11 x 47 mos =  81,174.17

Total cost = 216,789.79 + 81,174.17 = 297,963.96

Gotta be d the music of previous eras