it's very simple, all your Traditional, SEP and SIMPLE IRAs have to be lumped together and the value of each added together for a grand total year end value. ( I suggest you get the numbers from your December statements). There is no estimating. Use the value on Dec 31.
It sounds like you don't have SEP or SIMPLE IRAs, just traditional.
If you closed one in 2017, that one's contribution to the total is zero.
Tell TurboTax your basis of $6040. and what you took out during 2017 (that's your 1099-R) . TurboTax will do the calculations on Form 8606 for you.