Question

what are those two numbers whose sum is 58 and difference is 28

Answer 1

Let the two nos. be X and y.
wkt X+y=58 (equation 1)
x-y=28 (equation 2)
solving 1 and 2
2x=86
x=43
substitute X=43 in eqn 1
43+y=58
y=58-43
y=15