Question

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Doing some practice problems in a SAT book... D: but idk how to do this

Answer 1

Looking at this problem, you notice that the 1's place of the solution is the only thing that has a value. So your 'A' has to be larger than your 'B' (if they were equal or 'B' was larger you would have a solution in both places. Working off the premise that 'A' must be larger implies that you would borrow to do the subtraction--meaning that 'A' must be 1 larger than 'B' so that they will cancel each other.
This leaves only one value possible for 'C'.

Answer 2

ohhhhhh. omg, thanks :] ive been stuck on it for so long