Robert retired from the railroad after 50 years of service at age 70 in 2021. He is a widower and files as single. He received a Form RRB-1099 with $15,899 in box 5. He received a Form RRB-1099-R with $18,455 in box 7 and reports it on line 4d of his Form 1040/1040-SR. He received no other taxable income. Up to _____ of his Tier 1 benefits may be taxable