Mr. russell and ms. nicholson are teaching their classes how to write in cursive. mr. russell has already taught his class 2 letters. the students in ms. nicholson's class, who started the unit later, currently know how to write 4 letters. mr. russell plans to teach his class 3 new letters per week, and ms. nicholson intends to cover 2 new letters per week. eventually, the students in both classes will know how to write the same number of letters. how long will that take?