Scratch

Well...you could have it run through numbers until it reaches half the highest number or the lower of the two numbers...so for that example it would look a little like:
HCF:
set [HCF] to 1
set [count] to 0
repeat until (count) > number1
    change [count] by (1)
    if round(number1/count)=number1/count and round(number2/count)=number2/count
        set [HCF] to (count)
    end
end
say join ("The highest common factor is ") (HCF)

LCM would take a bit more, but you could have it work backwards, starting at number1*number2 and working down by intervals of number1 or something.