Answer: It will take him 1.68 years to recover his initial investment.
First, find the amount of extra money that he will make.
34,000 - 13,000 = 21,000
He will be making an extra 21,000 per year.
Now, divide the cost of his training by the amount of his increase.
35200 / 21000 = 1.68
That gives you the amount of years it will take him to pay off his investment.