Really it's not possible to offer anything but the most general observation given what you've posted. No-one can do anything but guess what the BankingAccount looks like, or the Startup class.
(Yes, we could guess that you're working on
CIS 211: Challenge Problem Set 3, but no-one is going to do that. You need to describe the problem clearly. It'll give others a clue and, more importantly, it'll clarify your own thinking.)
Work one method/constructor at a time. And justify each line of code you write in terms of what is actually stated in the question. Compile as you go and address compiler messages as they arise.
So, to begin with the new class's constructor:
public class MinMaxAccount extends BankingAccount{
private int holdMax;
private int holdMin=200;
public MinMaxAccount(Startup s) {
holdMax=s.startup_getBalance();
holdMin=s.startup_getBalance();
if(Startup s)
balance += c.credit_getBalance(); // (I advise you to use braces)
}
}
Why is
holdMin initialised to 200? (What part of the assignment instructions suggested that it should be?)
Does this code compile? If not, and you can't understand the compiler's messages, post them there. And post enough code and description that others can compile and see what you see.
-----
To repeat: don't rush headlong into code. Work one small step at a time, keeping to the assignment's instructions, and understanding and addressing the compiler messages.