I need help with my biology homework. Is anyone good at DNA questions?

You just need to keep in mind the mechanism by which DNA is "read". RNA translates it in codons, or groups of three bases. Mutations like the ones you mentioned above affect the reading of the codons in different ways. The major types of mutations are point mutations and deletion or insertion mutations. Generally speaking, point mutations (changing one base to another) are much less severe than the other two, because they change only one codon, whereas the insertion or deletion of a base shifts the "reading frame" of the DNA and changes all the codons after the mutation. In your question, this means that the insertion of the G at the beginning changes every codon in the sequence. The insertion of G in the middle changes every codon after that. (If G was inserted at the 3' end, nothing would change.) And the deletion of three bases means the deletion of an entire codon, so the reading frame is not shifted and the effect is simply a missing amino acid.