so let's name the numbers x and y.
we know that their sum, x+y is \(7\frac{2}{8}\)
and that that their difference, x-y is \(2\frac{4}{8}\)
so, from the last one we can find out x:
x-y=\(2\frac{4}{8}\)
x=\(2\frac{4}{8}\)+y
we can substitute this into the first one:
\(2\frac{4}{8}\)+y+y = \(7\frac{2}{8}\)
\(2\frac{4}{8}\)+2y = \(7\frac{2}{8}\)
2y=\(4\frac{6}{8}\) (7-2=5, but you have to "borrow" one because the fraction of the number from which you substract is smaller than of the other number)
so y=\(2\frac{3}{8}\)
then x will be
x=\(2\frac{4}{8}\)+\(2\frac{3}{8}\)
x=\(4\frac{7}{8}\)