From the information given, 4 added to the unknown number is equal to 2 times the unknown number when it is subtracted from 19.
Let the number be x
x + 4 = 19 - 2 (x)
We now expand and simplify the equation by placing unknown on one side and the known on the other side
x + 4 = 19 - 2x
x + 2x = 19 - 4
3x = 15
x = 15 /3
x = 5