It's y=kx. But 'k' is any constant. So my 'k' can easily be 1/(your k). The key is that when 'x' or 'y' increases by some factor, the other one also increases, by some constant multiple of the same factor. If so, then they're proportional.

<h2>
Explanation:</h2>
Remember you need to write complete questions in order to find exact answers. In this way you haven't provided any function, so I'll choose a quadratic function given by:

So we need to find the entire interval at which this function positive. Put another way:

By using graphing tool, we get the graph shown below. As you can see:
- The function decreases from

- The function increases from

- The graph of the function is a parabola that opens up.
But what is really importan in this problem is that:
- The function is positive over the interval

At this interval the function is positive, that is, 
<h2>Learn more:</h2>
Standard equation of the graph of a parabola:
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The actual size of the room is 8 feet by 20 feet.
Answer:
x = 29 degrees
Step-by-step explanation:
We know that all of the angles inside of a right triangle add up to 180. We also know that a right angle is 90 degrees. We can do 61 + 90 = 151. 180 - 151 = 29. This means that x = 29 degrees.