MLE of a Geometric Success Probability

A strategy is repeatedly tried until the first profitable fill. Let $X$ be the number of attempts until the first success, with support $1,2,\ldots$, and model $X\sim \mathrm{Geometric}(p)$.

If the sample mean from many independent episodes is $4$, find the MLE of $p$. Under the fitted model, what is the probability that at least 4 attempts are needed?