Question

What is the mass of an object whose weight is 80 newton

Answer 1

Weight = mg

m = Weight / g
= 80 N / (9.8 m/s²)
= 8.16 kg

Mass of object is 8.16 kg (or 8 kg if g = 10 m/s²).

Answer 2

If g=10
W=m×g
80=m×10
m=80/10
= 8kg