We had a solution to this problem from someone who didn't give their name or school - but thank you!

From the picture of the scales, the apple must weigh less than the four weights altogether.
If the apple weighs $180g$, for the scale to be balanced the weights would have to be $45g$ each because there are four of them. But we know from the picture that the apple weighs less than the weights put together, so each weight must be more than $45g$.
If the apple weighed $375g$, then for the scale to be balanced, each weight would be $93.75g$. So, for the weights to be heavier than the apple, each one must be more than $375g$.
One kilo is $1000g$ and four $250g$ weights would also weigh $1000g$ altogether so the scale would be balanced.