To determine the last point graphed on the first piece of the function \( f(x) = 2.5x \), we need to look at the domain of that piece.
The piece \( f(x) = 2.5x \) is valid for \( 0 \leq x \leq 20 \). Therefore, the last point on this piece will occur at the maximum value of \( x \), which is \( x = 20 \).
To find the corresponding \( f(x) \) value at \( x = 20 \): \[ f(20) = 2.5 \times 20 = 50. \]
Thus, the last point graphed on the piece \( f(x) = 2.5x \) is \( (20, 50) \).
So the final answer is: \[ (20, 50) \]