You know from the table that
500 seeds have an average of 4.4g. (You can ignore the leaf area as it's not asking about that)
All you have to do now is the proportion.
If 500 seeds weigh on average 4.4g.
That means 1 seed weighs 0.008g (just do 4.4/500)
So how much do 1000 seeds weigh? (0.008 times what?)