first, the numbers
245 = 5 * 7 * 7
49 = 7 * 7
the lcm is 5 * 7 * 7 because 5 * 7 * 7 has 5 * 7 * 7 (to make 245) and 7 * 7 (to make 49).
now the z's
the lcm of z^7 and z^8 is z^8
note: z^8 = z^7 * z
now the x's
the lcm of x^2 and x^6 is x^6
the lcm for the whole thing is 245(z^8)(x^6)