Question 328122
Here we are trying to calculate the age of Jan, Bill , and Sue. 

Remember Jan is one year younger than Bill, which makes him 1 year older than Jan.

Jan is one year older than Sue, which makes Sue one year younger than Jan. 

Let's assign an expression to each one of their ages:

Let x = Jan's age

Let x + 1 = Bill's age

Let x - 1 = Sue's age

The sum of everyone's age is 57. Now lets create our equation:

x + (x + 1) + (x - 1) = 57

Now lets simplify:

x + x + x + 1 - 1 = 57

Our ones cancel so we are left with:

3x = 57

Divide both sides by 3 and we are left with:

x = 19
 
So: 

Jan's age  is 19

Bill's age is 20 (19 + 1)

Sue's age  18 (19 - 1)

Check our solutions: 19 + 20 + 18 = 57 Yes!!!

Good Luck:-)