You exert a 0.98 n rightward force on a 2.43 kg cart.
a. what should the acceleration of the cart be without friction?

Explanation:

Newton's second law of motion describes the relationship between an object's mass and the amount of force needed to accelerate it.  

This law can be expresses as F=ma,

where  

The more mass an object has, the more force you need to accelerate it. And the greater the force, the greater the object's acceleration.

applying F=ma

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.