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