8c < - 64 ... c = what?

Well, you'll need to make it so that the c is alone. That means you'll have to get rid of the 8. To get rid of the 8 next to the c, simple divide each side by 8. - 64 divided by 8 is - 8, and 8 divided by it's self is 1. 1 is meaningless when it's multiplied, so you can just get rid of it, or hide it. So c is less than - 8, or

c<-8.