Answer:
The direct variation says that:
[tex]y \propto x[/tex] then;
the equation is of the form:
y = kx , where k is the constant of variation.
As per the given statement:
R varies directly with S.
By definition of direct variation:
[tex]R = kS[/tex]
Substitute the given values S = 16 and R = 80 to solve for k;
[tex]80 = 16k[/tex]
Divide both sides by 16 we get;
5 = k
⇒R=5S
Therefore, the constant of variation is, 5