simplify the expression, when adding or subtracting zero, the equation does not change -0.7 X +9 you remove the 0. but if you wanted to factor the expression you would have to convert the decimal number into a fraction zero -7/10 X +9 when adding or subtracting 0, the quality does not change -7/10 X +9 factor out of 1/10 form the expression 1/10 X (90-7X) or another way of writing it , 0.1 (90-7x)