Question 888323
The equation is x - 600 = 999. Add 600 to both sides to get



x - 600 = 999


x - 600 <font color="blue"> + 600</font> = 999 <font color="blue"> + 600</font>


x + 0 = 1,599


x = <font color="red">1,599</font>


The unknown number is <font color="red">1,599</font>