there are two point point a is on a mountain which is 5700 m above see level and the point b is in a mine which is 39600m below sea level. find the vertical distance between a and b

Since the point a is 5700 m above sea level; so the height of the point a = +5700 m
And the point b is 39600 m below sea level; so the height of the point b = -39600 m
Therefore the vertical distance between  a and b = $+5700-\left(-39600\right) = 5700+39600 = 45300 \mathrm{m}$