Retirement tax questions

For 401k plans see IRS publication 525 page 9.  The limit is 18,000 (24,00 if over 50)  for 401k plans
https://www.irs.gov/pub/irs-pdf/p525.pdf

For IRA Contributions the limit is 5,500 (6,500 if over 50) see Pub 590-A
https://www.irs.gov/pub/irs-pdf/p590a.pdf