Before an impulse can cross the synaptic gap between neurons, the impulse must be

In order for an impulse to cross the synaptic gap between the neurons, the impulse must be converted into a chemical signal as this will allow it to exert effects and to be able to travel in distances such as having to cross the synaptic gap between the neurons.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)