If a+b = -2 and x + y = -2 , what is 4x + 5a + 4y +5b

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?

Apack of gum would be considered a(n) necessity luxury item small ticket item unaccountable expense

Hello i need with my math homework i don't understand can someone explain how this works