Factorise x^2-16y^2 would be appreciated

Can someone me my sister? she is in third grade. 50 points and brainlist! ones that are not answered. plz and thx!

45% of the trees in a park are apple trees. there are 27 apple trees in the park. how many trees are in the park in all?

Suppose y varies directly with x. write a direct variation equation that relates x and y. then find the value of y when x=12 y=7 when x=3