What is a counterexample that shows the statement, the sum of two composite numbers must be a composite number, is false?

30 determine the coefficient on x 12 y 24 x12y24 in ( x 3 + 2 x y 2 + y + 3 ) 18 . (x3+2xy2+y+3)18. (be careful, as x x and y y now appear in multiple terms! )

Ageologist had two rocks on a scale that weighed 4.6 kilograms together. rock a was 0.5 of the total weight. how much did rock a weigh?

If a || b and b | y, then ? a) x || y. b) x | a. c) a | y. d) a || y.