Calculation Sum of two values

Hi,

I try to make a calculation of two values. But I didn't get a value.
I want to make a addition of the value Altersstruktur_u18 and Altersstruktur_1822. In the future I need also the same but for division.

public class testfor3_c {

private Id accId {get; set;}
public testfor3_c(ApexPages.StandardController stdcontroller) { 
    accId = stdcontroller.getRecord().Id;

    Altersstruktur_u18 = 0;    
    Altersstruktur_1822 = 0;  
    
    getEZRen();   
}

public Integer Altersstruktur_u18 {get; set;} // variable for people < 18
public Integer Altersstruktur_1822 {get; set;} // variable for people >= 18 AND <= 22
public Integer Sum_u18_1822 {get; set;}

public void getEZRen() {

List<Einzelrisiko__c> EZRList = [SELECT Alter__c, Jahresbeitrag__c, Alter_bei_Vertragsbeginn__c FROM Einzelrisiko__c WHERE Abgangsdatum__c = Null AND Unternehmens_Id_Long__c = :accId]; // create List EZRList with the information Alter__c of all people

FOR (Einzelrisiko__c EZR : EZRList) {  // Loop thru all people

    IF(EZR.Alter__c < 18) { Altersstruktur_u18++; } // if Alter__c < 18 variable Altersstruktur_u18 increase
    IF(EZR.Alter__c >= 18 && EZR.Alter__c <= 22) { Altersstruktur_1822++; } // if Alter__c >= 18 AND <= 22 variable Altersstruktur_1822 increase
    
} 

Integer Sum_u18_1822 = (Altersstruktur_u18 + Altersstruktur_1822);

}

}

Thanks in advance,
Sascha