The percent of the product would be 23
I believe that's is answer C because your ask about and increasment on the velocity in this observation
Answer: 
Explanation:
Multiply by t on both sides.
Now divide by I to isolate t.
Answer:
The volume of a given gas sample is directly proportional to its absolute temperature at constant pressure (Charles's law). The volume of a given amount of gas is inversely proportional to its pressure when temperature is held constant (Boyle's law).
17) 8.4 / 20 x 100
18) 20 . 0.5150
19) 6,50% because (as you said) the law of definite proportions states that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass
