Put the numbers into the point-slope equation and solve for $y$:

First, you find the slope:

Then, select one of the points in the exercise and put it together with the slope into the point-slope equation:

Since $b=0$, you know that the line passes through the origin. The function for the straight line is

To fill in the equation, you need values for $y_1$ and $f^{\prime }(x_1)$. You know that $x_1=3$, so $y_1=f(3)$ and $f^{\prime }(x_1)=f^{\prime }(3)$. We begin by computing $f^{\prime }(x)$:

Now you put this into the equation and get

You need the values of $f^{\prime }(x_1)$ and $y_1$. First, differentiate the function:

Now you can calculate $f^{\prime }(x_1)$. Since $x_1=0$, you get

You find $y_1$ by putting $x_1$ into $f(x)$:

You put all this into the equation and get