Answer:
6. constant force down
Step-by-step explanation:
drawing a free body diagram, and applying Newton's second law:
![\sum F=m.a\\\sum F=m*g*sin(\theta)](https://img.qammunity.org/2020/formulas/physics/college/m610q9gxwk62bj8ar1vu4qzdnynt0lduxm.png)
as you can see the only force playing a role on the box is the force done by the weight. all the values remain constant and so the force.
the correct answer is 6