Final answer:
Bill will be able to roll $10,000 into his IRA if he leaves White Drywall at the end of 4 years.
Step-by-step explanation:
White Drywall's retirement plan uses graded vesting, which means that the employee's ownership of the company's contributions increases gradually over time. In this case, since Bill has worked for 4 years, he will be entitled to 40% of the company's contributions to his retirement plan.
Therefore, Bill will be able to roll $10,000 ($25,000 * 40%) into his IRA if he leaves White Drywall at the end of 4 years.