Actually when u get a negetive value like u got here a= -80/3, you keep modulus to the
number or expression like this"|-80/3|",( the two dashes which are called as modulus) the function of modulus is to neglect any negetive values so that we can write in positve value,
example:- a = -80/3 when moudulus is placed |a|=|-80/3| which becomes a=80/3,
so my point is that when modulus is present from starting point of the question, if we remove the modulus from there(question) then the question becomes (+ or -) from there it self,
watch your question again if there is modulus present in it.