Hi. This is the solution to your qn. Basically, you break up 639 to form two numbers that are close to one another. These two numbers are just temporary numbers which you will use as a means of manipulation, to achieve your target of getting 1 as the smallest difference. From the manipulation, you will find out that you must subtract 39 by 38. Then, you should divide by 2 to equally add and subtract the numbers respectively. When you do addition on one number, make sure to do subtraction on the other. This is a principle you must know in order for you to arrive to your target. Hope this explanation helps you understand how to do the qn.