Hello,
[tex] x_{1} , x_{2} , x_{3} , ... x_{50} \\\\
\overline{x}= \dfrac{\sum_{i=1}^{50}\ x_{i}}{50} \\\\
\dfrac{\sum_{i=1}^{50}\ 53-x_{i} }{50} =-3.5\\
\dfrac{50*53 }{50} -\dfrac{\sum_{i=1}^{50}\ x_{i}}{50}=-3.5\\\\
53-\overline{x}=-3.5\\
\overline{x}=53+3.5=56.5\\
[/tex]
