the way i see it.. say you have 100km between two objects...
x is moving in a car at 60km/hr
y is moving in a car at 60km/hr, both heading towards each other
the formula would some something like
time = distance/velocity
distance (100km in this case)
____________________
(x speed + y speed)
= 100/120
=0.83hrs
times by 60 to convert to minutes
=50 minutes
i dunno..i only did the second lowest maths at school.. maybe im wrong