when 1 / 20 % of 4,000 is subtracted from 1 / 10 of 4,000 , the difference is
"( 1 / 10 ) * 4000 - ( 1 / 20 * 100 ) * 4000 = 400 - 2 = 398 answer d"
multiply(inverse(10), multiply(multiply(const_100, 10), add(const_4, const_4)))