Question: what is the highest common factor of 42 and 90?
Answer: The prime factorization of 90 is: 2 x 3 x 3 x 5. The prime factors and multiplicities 42 and 90 have in common are: 2 x 3. 2 x 3 is the gcf of 42 and 90. gcf(42,90) = 6.