S is in negative territory. So it is going to take you a distance to get to 0 and move further right to T.
You can do this without a formula just by adding 2 to get to zero and then 14 more to get to T. The distance between S and T is 14 + 2 = 16.
Now we should develop some kind of formula for these questions. When one point is on one side of zero on the number line and the other point is on the other side of zero then the formula for distance is
distance (as a formula for this question) = abs(S) + abs(T)
Distance = abs(-2) + abs(14) = 2 + 14 = 16
When both point are on the same side of zero then the formula becomes
Distance= abs(abs(S) - abs(T) )
For example if S = -2 and T = - 9
Then the distance = abs( abs(-2) - abs(-9) ) = abs(2 - 9) = abs(-7) = 7
If you have not taken abs value, then just take the answer that I have given above.