"when baby ian is held horizontally on his back, he sometimes makes an embracing motion by arching his back, extending his legs, throwing his arms outward, and then bringing his arms in toward his body. ian is demonstrating the " palmar grasp moro reflex tonic neck reflect babinski reflex

Moro reflex  

Explanation:

The baby has a series of reflexes in its first months of life and they are very important for the good development of the little ones. One of them is the Moro Reflex. In this reflection, the baby spreads his arms wide, stretches his legs and extends his neck. Moro's reflex begins from birth and continues until about four months of the baby. It occurs when the baby abruptly shifts position or falls backwards or feels in an insecure position, at which time the baby makes a hug movement by arching his back, extending his legs, throwing his arms out and then bringing his arms. towards the body.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.