regarding recent loan deferment but the loan interest still accrued

i'm confused with the interest calculation.

my monthly installment is 2000. Outstanding balance still left 400k and another 34 years to go
assuming my interest rate is 3% after deducted BR

A) 2000 x (3%/365x180) = total interest extra
B) 400k x (3%/365x180) = total interest extra
C) ????........

any idea what is the calculation formula and roughly how many extra interest i have to pay ?

would like take the deferment ?