Force = ma
Mass, m = 280g = 280/1000 = 0.28kg.
a = (-0.170i + 0.45j) m/s²
Since this is in vector form, let us find the magnitude of the acceleration.
a = √((-0.17)² + 0.45²). This is the formula for the magnitude using the vector components.
a = √(0.2314) ≈ 0.4810 m/s²
F = ma = 0.28 * 0.481≈ 0.13468
The force is ≈ 0.1349 N