Estimate s, the mutation rate for synonymous sites, from the given data. Mutation rates differ depending on

Question:

Estimate λs, the mutation rate for synonymous sites, from the given data.
Mutation rates differ depending on whether changing the nucleotide base changes the amino acid (non synonymous sites) or not (synonymous sites). A piece of DNA has 200 non synonymous sites with 12 mutations and 100 synonymous sites with 15 mutations. Our goal is to estimate the mutation rate.