1) It allows us to express an algorithm.

2) int 123; //invalid (sequence of numbers)
   int $50; //valid (but not conventional)
   int 50dollars; //invalid (starts with a number)
   int abs; //valid
   int hunter; //valid
   int @60cents; //invalid (illegal character AND starts with a number)
   int a_b; //valid
   int #define; //invalid (illegal character)

3)

public class Hello {
    public static void main(String [] args) {
        System.out.println("Hello, my name is Amara Auguste.");
        System.out.println("How are you?");
    }
}

4)
 
public class Arithmetic {
    public static void main(String [] args) {
        int a = 12; //arbitrary 
        int b = 10; //can be whatever values you want
        System.out.println("When a is " + a + " and b is " + b);
        System.out.println("The sum of a and b is " + (a + b));
        System.out.println("The difference between a and b is " + (a - b));
        System.out.println("The product of a and b is " + (a * b));
        System.out.println("The quotient of a and b is " + (a / b)); //integer division!
    }
}

5) 

1. Answer: 23
2. First compute: 5 * 2 = 10
   Next: 4 + 10 = 14
   Then: 14 - 3 = 11
   Answer: 11
3. Answer: 16
4. Result: 13
5. ((8 - ((2 * 4) / 2)) + 3) = 7
6. b = 10 + (2 * 3 - 1) = 10 + (6 - 1) = 10 + 5 = 15
   b = 15

6) 

MEMORY:
a = 10
b = 27
c = (10 + 27) = 37
d = (10 - 27) = -17
e = (10 + 27 * 3) = (10 + 81) = 91
f = (27 / 2) = 13 //integer division!
g = (27 % 10) = 7 

OUTPUT:
a is 10, b is 27
a+b is 37
a-b is -17
a+b*3 is 91
b/2 is 13
b%10 is 7

7) 

public class Rectangle {
    public static void main(String [] args) {
        int length = 22; //arbitrary
        int width = 18; //can be anything
        int area = length * width; //(l * w)
        int perimeter = 2 * (length + width); //2(l + w)
        System.out.println("Rectangle: length = " + length + " and width = " + width);
        System.out.println("Area = " + area);
        System.out.println("Perimeter = " + perimeter);
    }
}

8) 

public class Circle {
    public static void main(String [] args) {
        double radius = 7.5; //arbitrary radius, value can be changed

        double area = Math.PI * radius * radius; //(πr^2) OR Math.PI * Math.pow(radius,2)

        double circumference = 2 * Math.PI * radius; //(2πr) 

        System.out.println("Radius: " + radius);
        System.out.printf("Area: %.3f\n", area);
        System.out.printf("Circumference: %.3f\n", circumference);
    }
}