Or adding nine to both sides, we get y to the fourth power is equal to 16. And this would tell us that y is going to be equal to plus or minus two. Well, there would be then two horizontal lines. One would be y is equal to two. The other is y is equal to negative two. But they want us the equation of the horizontal line that is tangent to the curve and is above the x-axis. So only this one is going to be above the x-axis.