Correct answer - 120 for Thymine.
Why? - 320 Nitrogen bases.
Cytosine = 40, Cytosine = Guanine.
Therefore Guanine = 40.
320 - 80(Cytosine and Guanine)
240.
Adenine and Thymine = ?
Adenine = x and Thymine = x.
2x = 240.
X = 240/2
X = 120.
Adenine 120, Thymine = 120, Cytosine = 40 and Guanine = 40.