Sandrine is now able to use abstract thought as well as logic; Piaget would argue that she is in the stage of development.

formal operational

Explanation:

Jean Piaget, a Swiss developmental psychologist, propounded the theory of cognitive development which explains how an individual gradually create, acquire, and use knowledge as the individual interacts with his environment right from birth. Piaget describes the cognitive development of an individual in four stages, which are the sensorimotor, preoperational, concrete operational, and formal operational stage of cognitive development.

The final stage of cognitive development is the formal operational stage, where Piaget describes development taking place as from the 11 years  of age of an individual. At this stage, he posits that a child begins to use logic in understanding abstract ideas and concepts, as well as engage in problem-solving.

9, 5, 10000000 ( that is supposed to be a ten for the last one)