Answer:
27 N
Step-by-step explanation:
Since force varies directly with acceleration, we can introduce a constant, k, and write [tex]F=ka[/tex]
When force is 15, acceleration is 5, so plug it into the equation and solve for k:
[tex]F=ka\\15=k(5)\\k=\frac{15}{5}\\k=3[/tex]
Now, to find force, we use a = 9 and k = 3, so
[tex]F=ka\\F=(3)(9)\\F=27[/tex]
The force is 27 N