Picture a number line. the starting point is 0. go forward 5 which brings u to 5 on the number line. then since he lost 7 go back 7 which brings u to -2. now to get back to 0 you need to go forward 2. which means that he must gain 2 in order to get back to the starting point.
6 x 10^-3 because the decimal point is 3 place value units away from the 6, and scientific notation is a x 10^n, where n can be a positive of a negative depending on the number
