The free-energy change for the formation of a protein from the individual amino acids is positive and is thus an endergonic reaction. how, then, do cells accomplish this process?

An endergonic reaction, like photosynthesis, refers to a reaction, which needs the energy to be driven. The activation energy for the reaction is usually greater in comparison to the entire energy of the exergonic reaction. The endergonic reactions are non-spontaneous.  

In the given case, in order to accomplish the process, the coupling of the endergonic reaction, that is, thermodynamically unstable reaction with an exergonic, that is, the thermodynamically stable reaction is done so that the entire free-energy change of the coupled reactions becomes negative.  

the two answers are a, the population of birds with large beaks will increase on the island, and c, the trait for large beaks will be passed on to future generations through natural selection. the reason for that is because if the birds that have beaks developed for eating small seeds lose all of their food, they will go hungry and eventually starve because they physically cannot eat the large seeds, therefore making the population of large beaked birds higher. also, if the trait of large beaks are dominant on the island over small beaks, then over time the large beaked birds will reproduce more and more, while the smaller beaked birds will reproduce less and less because they can't survive with the food provided. that leads to the trait of small beaks disappearing and the trait of large beaks taking over the island.