Question

Which is an equation of a direct proportion?
y=16x+6

y=6x

y=6x−6

y=6x

Answer 1

The model for direct proportion is y = mx.  Note that there is no "offset," no "y-intercept."  

y = 6x represents direct proportion with a constant of proportionality 6.  The other 2 choices are disqualified because of offset +6 or -6.