Imagine those two numbers on the number line, and notice that they are separated by 102 - 86 = 16 units.
So the middle point in between the two will be located 16/2 = 8 units to the right of the smaller number, that is:
86 + 8 = 94
The number midpoint is 94
Now, we can use directly the formula for midpoint between two numbers x and y with x being the smaller one:
midpoint = x + (y-x)/2
So in our case x is 86 (the smaller of the two numbers) and y = 94
then the midpoint is:
midpoint = 86 + (102 - 86)/2 = 86 + 16/2 = 86 + 8 = 94