54. In a certain exam, Xiao Ming's scores in mathematics, Chinese, English, physics, chemistry, and biology are $x$, 85, 85, 94, 89, 91 respectively. If the scores of these subjects are made into a pie chart, the central angle corresponding to Xiao Ming's mathematics score is $64^{\circ}$. What is Xiao Ming's mathematics score? $\qquad$
Reference answer: 96