As y=bx, what factor can cause b rising in the equation of dy/dx=df(x)/dx=d(bx)/dx=b?

dy/dx=lim(h->0) [f(x+h)-f(x)]/h
dy/dx=lim(h->0) [b(x+h)-bx]/h
dy/dx=lim(h->0) bh/h
dy/dx=lim(h->0) b
dy/dx=b
The slope is positive number and x value is positive number