### This one should be easy... just need help with interest formula.

I created the "banking program" below, I just need help calculating additional interest. Interest is automatically added into the balance if they choose over 1000 deposit and more than 12 months, but I am trying to add a while loop that allows them to add additional interest if they want it. Everything works, I just don't know the right formula for the additional interest. Please look below and tell me where I went wrong.
Thank You! Line 51 is what I am having problems with, it shows the new interest, but the total is wrong when I test it.

 ``123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566`` ``````#include using namespace std; int main () { int duration; double interest; double amount; char account; char answer; int additional; do { cout << "How much will you like to deposit? >> "; cin >> amount; cout << endl; cout << "What's your preferred account type" << "\nEnter S for saving or C for checking >> "; cin >> account; cout << endl; switch (account) { case 'c': case 'C': interest = amount * 0.05; break; case 's': case 'S': interest = amount * 0.10; break; default: cout << "\nInvalid account type. Try again!" << endl; cin.get(); cin.get(); return 0; } cout << "Enter the time duration in months >> "; cin >> duration; cout << endl; if (duration >= 12 && amount >= 1000) cout << "Amount Due = \$" << amount + interest << endl; else cout << "Amount Due = \$" << amount << endl; cout<<"How much additional interest would you like?"<>additional; cout<<"Your new interest is>>"<> "; cin >> answer; cout << endl; } while (answer == 'y' || answer == 'Y'); cout << "\nProgram terminating..... bye !!!" << endl; return 0; } ``````