fit evenly basically means does the runner need to take a whole number of steps to complete the race, assuming the runner travels a consistient distance per stride
easy way is
is 138435 divisble by 3?
a hack to tell if a number is divisble by 3 is to add the digits and if the sum is divisble by 3, it is divisble
1+3+8+4+3+5=24
24 is 3 times 8
it is divisible by 3
yes