There are 7 red cubes. there are 8 yellow cubes. how many cubes are there in all ? use a double to add write the missing number

hello from mrbilldoesmath!

answer:

x - 3

discussion:

x^2 - 9 = (x-3) (x+3)   so

(x^2-9)/ (x + 3) = x-3

you,

mrb

not sure but it may be b, as i said i'm not sure.