Help me! new to programming and can't figure this out!

For one of my assignments we have to create a class to determine the Total Tax Revenue one two houses. I have created the class and the Test class as well but I cannot seem to get the total tax revenue from the two houses.

I will put the class and test class as well.

I will put the ? mark where I do not know what to do in.

Also the testclass was given, we were just assigned to make up the class so i can't make any changes to the testclass.

please help i kno this is probably an easy solution for experienced programmers, but for someone who just started a week ago, its hard!

public class PropertyTax
{
private double assessedvalue;
private double taxrate;
private static double taxableamount;
private static double propertytax;
private static double totaltaxrevenue;

public PropertyTax(double AssessedValue, double TaxRate)
{
assessedvalue = AssessedValue;
taxrate = TaxRate;
taxableamount = assessedvalue*.92;
propertytax = taxableamount*(taxrate/100);
totaltaxrevenue = ??????????;



}
public double getAssessedValue()
{
return assessedvalue;
}

public double getTaxRate()
{
return taxrate;
}

public double getTax()
{
return propertytax;
}

public double getTaxableAmount()
{
return taxableamount;
}

public static double totalTax()
{
return totaltaxrevenue = ??????;
}

public double calculate()
{
return propertytax = taxableamount*(taxrate/100);
}
}

import java.text.NumberFormat;

class TestPropertytax
{
public static void main(String[] arg)
{
NumberFormat nf = NumberFormat.getCurrencyInstance();

PropertyTax p1 = new PropertyTax(100000, 1.05);
p1.calculate();
print(p1, nf);
System.out.println("----------------------------------");

PropertyTax p2 = new PropertyTax(150000, 1.05);
p2.calculate();
print(p2, nf);
System.out.println("----------------------------------");

System.out.println("Total tax revenue " + nf.format(PropertyTax.totalTax()));
System.out.println("--------- End of report ----------");
}

static void print(PropertyTax p, NumberFormat nf)
{
System.out.println("Assessed value " + nf.format(p.getAssessedValue()));
System.out.println("Taxable amount " + nf.format(p.getTaxableAmount()));
System.out.println("Tax rate for each $100.00 is " + nf.format(p.getTaxRate()));
System.out.println("Property tax is " + nf.format(p.getTax()));
}
}