micro c code for speed calculation using IR sensors

[Monetary Monetary]

hie guys, need your help to calculate speed taken by a moving vehicle and display it on LCD.it passes through two pairs of IR sensors which are a fixed distance apart using timers in PIC 16F877A with a 20Mhz oscillator i am using micro c.
it activates timer when it passes 1st sensor and deactivates timer when it passes 2nd sensor but how do i find time taken in micro c

 

[kam1787]

can you not derive the time interval from the timer?

another way is to save the time from the 1st sensor, and then save the time from the 2nd - the difference is the time interval