Hello, I am having trouble understanding why solving this problem algebraically does not provide me with the correct answer (I keep getting 60). I solved the problem by adding and subtracting the 10 to the original ratio (5:3) and equating it to the new ratio (7:5). Because I already added and subtracted the 10 in the problem, I shouldn’t have to do it again right?

You got x correctly. ~~I don’t understand the rest of your steps: why are you finding 7\times 30 : 5 \times 30 and how did you conclude that to be equal to 60? Notice that you have a ratio…~~

Edit: I see what’s going on. (5x - 10) and (3x + 10) are the number of stamps - 7x and 5x are just the final ratio (in fact, most answers wouldn’t even include the x there)