How many newtons equals 31.5 grams?

That depends on how much those 430 grams are accelerating. Newtons are a measure of force, which is equal to the product of mass and acceleration. We are given the mass, but not the acceleration, so we have no way of knowing the number of newtons involved.

One might assume however, that the force you are looking for is that of gravity. In that case, the acceleration would be approximately 9.8 m/s2. Newtons are equivalent to kilograms times meters per second squared, and 430 grams is equal to 0.43 kilograms. The amount of force then, would be (0.43 * 9.8) N, or 4.214N.