If you have 10 red balls, you have blue balls in proportion 3:2, so you have 15 blue balls. Moreover, you have white balls in proportion 8:2=4:1, so you have 40 white balls.
Removing 10 white and blue balls causes you to have 30 white, 10 red and 5 blue balls.
Since 30=5*6 and 10=5*2, the new proportion of white, red and blue balls is 6:2:1.
a difference is the result of subtraction. while each of these expressions has subtraction in it, a difference will be the result when subtraction is the last operation applied in the order of operations for the expression. this means subtraction must be outside of the parenthesis. only b has this.