Given:
8.90ft³ for 30 balloons
Let h be the volume of helium and b be the number of balloons.
Using proportion;
b/h = 30 /8.90
Multiply both-side by h


Hence, the answer to blank 1 is the above.
when b=50, substitute for b in the above and solve for the volume (h).
That is;

Multiply both-side by 8.90/30


Hence, the answer to blank 2 is 14.83ft³.