Step-by-step explanation:
This question is a bit unclear. I think it's two questions conjoined. Anyways,
F=m×a
F=100N
a=10m/s^2
m=?
Making m the subject of formula
m=F/a
Substituting we have,
m= 100/10
m=10kg
Using the formula for m above
F=280N
a= 0.5m/s^2
m=?
m=280/0.5
m=560kg
Let's check our answers
F=m×a
F=10kg×10m/s^2
F=100N
Correct✓
F=560kg ×0.5m/s^2
F=280N
Correct✓
I hope this is timely;-)