The highest common multiple??? That would be infinity...
Highest common factor? That would be the product of shared primes of the numbers prime factorization...
16=2*2*2*2, 24=2*2*2*3 so the product of shared primes is 2^3=8
So 8 would be the greatest common factor
Least common multiple?
That would be the product of the highest occurring primes in their prime factorization...
16=2*2*2*2, 24=2*2*2*3 so the product of highest occurring primes is:
2*2*2*2*3=48
So 48 would be the least common multiple....
The "highest common multiple" would be 48n where n would approach infinity so it would be +oo