How to find the median of 57, 68, 70, 85, 88, 88?

Since they are already in numerical order, all you need to do is find the middle number. There is an even number so you will have to find the average. Take the middle two numbers, $70$ and $85$, and find the average.
$\frac{70 + 85}{2} = 77.5$
The median is $77.5$.