The constant of proportionality in this relationship is 5.6.
Proportional relationship:
Proportional relationship is a relationship between two variables where there ratios are equivalent.
The variables are as follows:
v = the volume of a sample of helium in litters
m = the mass of that sample in grams
Therefore,
v = km
where
k = constant of proportionality
Therefore,
k = 28 / 5
k = 5.6
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