Answer: 0
Reason:
The graph starts off very steep at x = 0. As x increases, the steepness goes down. Meaning the tangent lines become more shallow as you move to the right.
This tells us that the person learning the new task learns a lot at first. Then as time wears on, they learn less and less, until leveling off at some plateau.
If your teacher has covered derivatives, then you'll find the derivative of y = 1-e^(-0.28x) is dy/dx = 0.28e^(-0.28x)
Graph this derivative function using something like GeoGebra. Notice how the derivative curve is always decreasing. Therefore, x = 0 is when the derivative is largest, which points to the original function having the steepest increase (aka largest instantaneous rate of change).
See the graph below.