1099-r. taxable income says unknown, and box 7 is 3-disability. I am 67. How do i calculate taxable income?

If you didn't contribute to the plan from your own money, that is money you paid tax on, then all of it would be taxable. If you made contributions from your own money, there would be an amount in box 9b of your Form 1099-R which would show your contributions.  

In that case, after you enter your Form 1099-R, you will see a screen that says Describe the Taxable Amount, on which you have to choose  No, a different amount was taxable:

On another screen you will see the option to choose the Simplified method or General rule method to determine how much of your pension distribution is taxable: