John’s backyard vegetable garden measures 30 ft by 40 ft, hence, its area is 30 × 40
= 1200ft2
. He decides to make it longer, so that the area increased to A = 30 (40 + x).
Which property of real numbers tells us that the new area can be written A = 1200 + 30
x?
distributive
really -- there are only a few properties to choose from ...