The numerical coefficients of the given monomials are 42 and 63. The greatest common factor of 42 and 63 is 21.The common literals appearing in the two monomials are x, y and z. The smallest power of x in the two monomials is 2.The smallest power of y in the two monomials is 1.The smallest power of z in the two monomials is 1.The monomial of the common literals with the smallest powers is x2yz.​Hence, the greatest common factor is 21x2yz​.