Zeros or roots of a function is the value of independent variable (usually x - coordinate or absicca) where the value of dependent variable (y - coordinate or ordinate) is 0.
That is :
The point where it cuts the x - axis, it has an x - coordinate = -6
Therefore, we can conclude that The zero of given function is -6
Curt because if his time was 8/9 of Ian's time then that means he ran the mile in a fraction of Ian's time, so he finished the mile quicker. Curt ran faster.