CALCULATE HOW MUCH TIME IT TOOK TO MAKE IT TO THAT DISTANCE THEN USING THE TIME YOU MADE IT, WE'LL SUPPOSE THAT THE RACE IS 100M IN LENGTH. YOU SHOULD TRY TO GET BOTH NUMBERS AS ACCURATE AS POSSIBLE. INACCURATE NUMBERS WILL MAKE YOUR FINAL CALCULATION A LITTLE BIT OFF.
DIVIDE THE NUMBER FOR THE DISTANCE BY THE AMOUNT OF TIME IT TOOK TO ARIVE TO THAT DISTANCE AN EASIER WAY TO. SAY IT IS SPEED = DISTANCE/TIME OR S=D/T.,THE EQUATION IS READ : S=100M/12SECONDS. YOUR SPEED WOULD BE ABOUT 8.3 MPS