37.3g is correct

The first rider is on 30g.

The second rider is on 0g.

The third rider is on 7.3g.

You add all these numbers up to get 37.3 g.

263.5g is correct

The first rider is on 60g.

The second rider is on 200g.

The third rider is on 3.5g.

You add all these numbers up to get 263.5 g.

536.8g is correct

The first rider is on 30g.

The second rider is on 500g.

The third rider is on 6.8g.

You add all these numbers up to get 536.8 g.