Gamma scale MLE with shape four

Rainfall accumulations are modeled as independent Gamma variables with known shape $k = 4$ and unknown scale $\theta$, density $f(x \mid \theta) = \dfrac{x^{k-1} e^{-x/\theta}}{\Gamma(k)\,\theta^{k}}$ for $x > 0$. A record of $n = 10$ storms totals $\sum_i x_i = 80$ millimeters.

Find the maximum likelihood estimate of the scale $\theta$.