There are a few answers but an example of one could be 7^10 * 7^5
hope this helps
Oder of operations is this;
The C(x) equation is a parabola with a squared "x" and a positive leading term coefficient, meaning, is a vertical parabola and it opens upwards
the lowest point, or lowest cost value, it reaches, is the U-turn point, or vertex

so, the lowest cost is at