To solve this problem we must know that when any two lines intersect , a pair of opposite angles from the figure Will be equal
so that means that

we can subtract twenty from each side


now we can subtract like terms

so we can get the final answer as
There is no difference, 6rs-(-2rs) if you get rid of the parenthesis you are left with 6rs- -2rs and two negatives make a positive therefore the answer will become 8rs... I hope this helps :)