Lex watched the balloon filling with Helium, maintaining a tight enough grip to ensure the balloon didn't shoot right away from her wand and force her to start over. It wouldn't be too hard, given the light matter being conjured but that was besides the point. The first attempt would have been rendered a waste and there was little the Gryffindor hated more.

It'd been a while since she'd seen a whole watermelon but that didn't mean she couldn't estimate. It only needed a little more....just...a little....there! "Finite."

Lex tied her balloon shut, keeping the air from slipping back out then headed to the Professor's desk for a radiosonde. How this would help them get aireborne she still didn't know but again, blind faith. They would be going up in hot air balloons and it would be epic. It was all a matter of patience and waiting. As she got back to her seat she found one of the baby 'Claws making their way over to her.

Oh?

Ah, that explained it perfectly. Help. They were meant to be helping afterall and something like this wasn't tremendously difficult for her to begin with so it was hardly a burden. " 'Course I can help you." She said with a grin. Oh but first. Lex put her balloon below her desk to prevent it from floating away then took another from the pack.

"First thing's first, you'll wanna secure it so it doesn't dart off like half these balloons have." She said, gesturing to the way she'd held her own balloon just now. "Then comes the harder part," for the younger ones anyway, "the conjuring of helium."

Lex gave a light flick of her wand, eyes on Penelope to be sure she was watching. "It'll take a bit of concentration and that flick then the incantation. Try to calm down and really focus." Go ahead, give it a shot. It'd be fine if she didn't get it straight away. Lex wasn't in a rush.