I answered ALL your 15 problems. Sorry, I took long.
Please mark me brainliest if this helped you. That will help me a lot ...
I hope it helps!

Cross multiply:

Divide by h on both sides:
Answer:
Ratio should be equal so ratio is 3:3
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Answer: 285.2 kg
Step-by-step explanation:
Given
The volume of helium in the balloon is 
The density of the helium is 
Mass of the helium gas is given by the product of density and volume

Thus, the mass of gas is 285.2 kg
Answer:
30 weeks
Step-by-step explanation:
7.25 x 20 = 1 WEEK
1 WEEK= 145$
4,350 divided by 145=30
30 weeks