F = ma
Rearrange this so acceleration is the subject:
A = f/m
Now input your values into this equation for the first question :
A = f/m
A = 15/45
A = 0.33333333 m/s
Then using this same equation change the force of 15 to 25 :
A = f/m
A = 25/45
A = 0.55555556 m/s
For the last question keep the force of 15N but change the mass to 70kg into the same equation :
A = f/m
A = 15/70
A = 0.21 m/s (rounded)
A centre - seeking force related to acceleration is centripetal force.
Im pretty sure the answer is A.