Does anyone have an equation to calulate travel time?

As an example I need help with my intercepts. I see a convoy moving at X speed at Y bearing. How can I calculate how long it will take to travel a certain distance so I can plot an intercept better? I need to be able to figure out how long it takes to travel a certain distance at certain speeds so I know if I will be fast enough or whatever to get at the target, ahead or behind. Whatever the case may be.