The last point graphed on the first piece of the function, \( f(x) = 2.5x \), occurs at the upper limit of the domain for that piece, which is when \( x = 20 \).
To find the corresponding \( f(x) \) value at \( x = 20 \):
\[ f(20) = 2.5 \times 20 = 50 \]
Therefore, the last point graphed on the first piece of the function is:
\[ (20, 50) \]