Which of the following equations have exactly one solution? Choose all answers that apply:

A: -19 + 18 = -19x+ 18

B: 19x + 18 = -19x + 18

C: -19x – 18 = -19x + 18

D: 19x - 18 = -19x + 18

The line plot below represents the number of letters written to overseas pen pals by the students at the waverly middle school. each x represents 10 students. how many students wrote more than 6 and fewer than 20 letters. a.250 b.240 c.230 d.220