Solve this 6r+7=13+7r

Let's move all to one side:

6r+7-13-7r=0

and re-arrange  to have similar terms together:
6r-7r +7-13=0

let's add up what we can:

-1r-6=0
we can move the -6 to the other side and multiply both sides by -1 and we get:
r=-6 This is the solution. 

Hello!
your answer should be c