To identify which equation has a constant of proportionality equal to \( 10 \), we need to analyze each option. The constant of proportionality \( k \) in a direct variation equation of the form \( y = kx \) is simply the coefficient of \( x \).
Let's simplify the coefficients for each choice:
-
Choice A:
\[ y = \frac{2}{20}x = \frac{1}{10}x \quad (k = \frac{1}{10}) \] -
Choice B:
\[ y = \frac{30}{3}x = 10x \quad (k = 10) \] -
Choice C:
\[ y = \frac{12}{2}x = 6x \quad (k = 6) \] -
Choice D:
\[ y = \frac{5}{5}x = 1x \quad (k = 1) \]
Among all the choices, Choice B \( y = \frac{30}{3}x \) simplifies to \( y = 10x \), which has a constant of proportionality equal to \( 10 \).
Thus, the answer is Choice B.