If a tree has 24 light rings and 24 dark ring how old is it

the tree is 24 years old. The inner part of the stem of the tree has a part referred to as cambium. Each year cambium produces high number of cells with thin cell walls when tree is highly active. These cells form the light-colored  rings. When tree is less active cambium synthesizes few small cells with thick walls. The region occupied by these cells appear as a darker ring on the cross section of the stem. These two processes occur in the same year and as result each growth year is characterized by a ring consisting of a light and dark parts.  

Um can u take a picture of the work