When it says "the subject", it only means you need to isolate the x, or solve for x. To do that, we have to get the x by itself. But how can we do that? We'll have to get rid of that pesky -5. Well, what can we do to -5 to get to 0? Of course -- Add 5!
b=x-5
+5
But whatever we do to one side of the equation, we have to do to the other.
b=x-5
+5 +5
We're left with b+5=x. There's your answer!
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