Who is the highest common factor of 21 and 42? And who is the highest common factor of 28 and 56? If r represents the least common multiple of p and q, then which of the following statements is true?
a. For 21 and 42, the highest common factor is 21. For 28 and 56, the highest common factor is 28. The statement r = p * q is true.
b. For 21 and 42, the highest common factor is 3. For 28 and 56, the highest common factor is 28. The statement r = p * q is true.
c. For 21 and 42, the highest common factor is 7. For 28 and 56, the highest common factor is 14. The statement r = p * q is false.
d. For 21 and 42, the highest common factor is 1. For 28 and 56, the highest common factor is 28. The statement r = p * q is false.