Question 713478
Hundred's digit: x+4+2
Ten's digit: x+4
Unit's digit: x

13= (x+4+2)+(x+4)+(x) : Simplify
13-4-4-2 = x+x+x
3=3x : Divide both sides by 3 to get the value of x
3/3 = 3x/3
1=x

Hundred's digit: x+4+2
=1+4+2
=7
Ten's digit: x+4 
= 1+4
= 5
Unit's digit: x =1

Answer: 751