Question 932956
Let x = the first number
    y = the second number

The sum of two numbers is 75.
x+y=75

The difference between those numbers is 21.
x-y=21

x+y=75
x-y=21
 2x=96
  x=48

Substitute x with 48
48+y=75
   y=75-48
   y=27

The numbers are 27 and 48.

Check
48-27 = 21
   21 = 21