To find the last point graphed on the first piece of the function \( f(x) = 2.5x \), we need to look at the domain of this piece of the piecewise function, which is defined for \( 0 \leq x \leq 20 \).
The last point of the first piece occurs at the upper limit of this interval, when \( x = 20 \). To find the corresponding value of \( f(20) \):
\[ f(20) = 2.5 \times 20 = 50. \]
Thus, the last point graphed on the first piece of the function is \( (20, 50) \).