The y-intercept of the graph of a function is the point at which the graph intersects the y-axis. In other words, it's the value of the function when x=0.
So to find the y-intercept of f(x) = 57(3.2)x, we can substitute x=0 into the function:
f(0) = 57(3.2)(0)
f(0) = 0
So the y-intercept of this function is (0,0).