Atwo digit number is seven times the sum of its digits. the tens digit is 3 more than the units digit. what is the number

let x =  the tenth digit   and y the unit digit 

is seven times the sum of its digits.  7( x+y)  = 10 x +y 
7x + 7 y = 10x + y
3x =  6y     x= 6y / 3 = 2y    x= 2y 

we have that the tens digit is 3 more than the units digit so 
x = 3 + y
we replace it in the first equation   x= 2y
  3+ y = 2y 
 y=3 

and x= 6 
so the number is  63