How to determine SS taxable amount

I have a SSA-1099,Benefits paid in 2019= $31,744.80 (Box#5)

Box #4 Benefit Repaid =None, Part B Premiums Deducted = $5,200.80. Prescription Drug Part D Deducted = $850.80, Federal Tax withheld = $3,584.40.

??? On My 1040-SR Form,

Block#5a shows my SS Benefits ( $31,745 )

Block 5b shows a the taxable amount  of $14,801.

How did turbo tax arrive at that taxable amount,when my total SS benefit was $31,745.00, and most importantly is the amount correct.

Thank You

Richard