Factorise 4(x - y)^2 -9(x + y)^2​

Me. i can't figure out this question. give an explanation too. .

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

Multiply sixth of sixty six by a half of ten show step by step method