Twice the difference of 9 and a number.

Answer 1

2(9-x)

or 2(x-9)

but usually the convention is to make the difference positive

so write it as the absolute value of x-9 or 9-x

2l9-xl = 2lx-9l

absolute value is always the positive difference

if x is 19 then 2l9-19l= 2(10) = +20

and 2l19-9l= 2(10) = +20

the absolute value sign is just two vertical lines at the beginning and end of the terms