MLE with Right-Censored Exponential Data

A venue studies the time to the next spread-widening event. Eight observation windows are each followed for up to 5 seconds. In total, 5 windows contain an event before 5 seconds and 3 windows are right-censored at 5 seconds. The total observed exposure time across all 8 windows is 40 seconds.

Model event times as i.i.d. $\mathrm{Exp}(\lambda)$ and find the MLE of $\lambda$.