Pensions Line51b 1040

I have entered 3 1099Rs. 2 pensions and 1 IRA RMD. The sum of those 3 is correct and shown on line 5a 1040. But on line 5b shows a reduced taxable amount. I do know of any reason for any of it to be non taxable. Last years 1040 did not show 2 amounts, only an amount on 5b. Please help.