Xavier is a strange boy who is very secretive but has been very useful to the kids in the palace.
He has a flying machine called the aerotrope which he use to fly around the flooded city of grimsdon and he can use it to fly to buildings to scavenge for supplies and go to the outskirts of grimsdon.
He also knows about the haggle which they can use to trade supplies for other supplies.
The only thing is that Griffin suspects him of something or of betraying him but every one else is fine with him.

Step 1: Find a tall object to measure.
Step 2: Point the astrolabe at the top of the object and look though the straw.
Step 3: Make sure you get it on 45 degrees and get someone to help you see the degrees.
Step 4: Then get a measuring tool like a meter ruler or a tape measure to measure the object.
Step 5: You must measure how many meters it is away from you when you are at a 45 degrees.
Step 6: Calculate how tall you are from your feet to your eyes.
Step 7: Add your height and the distance to the base of the object. This answer is the height of the object.

Isabella has to choose between two sacks to trade at the haggle but she can't decide.

In the first sack there is a snorkel, spear gun, iPod, gemstone necklace, guitar and toothpaste. The good things about this sack are that the snorkel and spear gun would be good for hunting under water. The toothpaste would be good for their teeth the guitar and iPod would be great for entertainment  but it would not be very useful and the gemstone necklace would be nice but again not useful.

In sack two there are a deck of cards, seven cans of peach slices, life jacket,bow and arrows, binoculars and a water filter. The bow and arrows would be good for fending off a thief, the peach slices would be a welcomed meal binoculars would be great for looking out on the city, the life jacket is a great replace meant  one of them breaks and the water filter would clean flood water.The deck of cards would be fun but it would not help with their survival.

I think sack two would be better because it has more useful supplies and only has one item with no benefit to the kids in the palace.