Possible integer factor pairs of 64: $(1, 64), (2, 32), (4, 16), (8, 8), (16, 4), (32, 2), (64, 1)$.
Sums: $65, 34, 20, 16$.
Only possible sums = 65, 34, 20, 16. Since 65 is listed as “cannot be” but is possible, the only impossible option is 35. However, question asks which cannot be → 35 is impossible. So answer is (d).