Write a system of equations to describe the situation below, solve using substitution, and fill in the blanks. Mr. Watson and Ms. McKee are teaching their classes how to write in cursive. Mr. Watson has already taught his class 3 letters. The students in Ms. McKee's class who started the unit later, currently know how to write 12 letters. Mr. Watson plans to teach his class 4 new letters per week, and Ms. McKee intends to cover 3 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? How many letters will the students know? In _____ weeks, the students in both classes will know how to write _____ letters In cursive.