The function values for h(x) vary directly as x for all real numbers. The graph of y = h(x) in the standard (x,y) coordinate plane is:

a line with a y-intercept at 0.

How do they get this solution and why can't it be the other possible solutions which are:

a line with a y-intercept but not at 0

a line with no y-intercept

a hyperbola

neither a line nor a hyperbola