In the picture, how old is X?

B - between 100 and 500 million year old.

Explanation:

Because X is older than the 100 layer but younger than the 500 layer according to the position in the picture.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.