Question:  

Implement a super class Person. Make two classes, Student and Instructor
that inherit from Person. A person has a name and a year of birth. A student
has major and the instructor has a salary. Write the class declarations, the
constructors, and the methods to String for all classes. Write a test program
that tests these classes and methods.

This may not be a complicated one but i'm a beginner in java. Please help me.
I'm getting the following error at the both the constructors 'student()' and 'instructor()'.

```
"constructor Person in class Person cannot be applied to given types;
  required: String,int
  found: no arguments
  reason: actual and formal argument lists differ in length."

```

Here's my code:

```
package One;

class Person{
    String name;
    int yob;

    Person(String s, int d){
        name = s;
        yob = d;
    }
    @Override
    public String toString(){
        return "Name: "+name+"\n Year of Birth: "+yob;
    }
}
class Student extends Person{
    String major;

    Student(String s){
        major = s;
    }
    @Override
    public String toString(){
        return "The student did his majors in "+major;
    }
}
class Instructor extends Person{
    int salary; 

    Instructor(int a){
        salary = a;
    }
    @Override
    public String toString(){
        return String.format("The salary is ",salary);
    }
}

public class Test {

    public static void main(String[] args) {
        Person p = new Person("Stephen", 1991);
        System.out.println(p);
    }
}

```

Thanks in advance.