let the digit in the tens place be x and digit in the one's place be y.
So according to the question
x=3y .....(1)
And the original number = 10x+y
and the new number when digits are interchanges=10y+x
So according to the question
(10x+y)+(10y+x) = 88
11x+11y=88
x+y=8 ...(2)
Putting equation (1) in the equation (2) we get
3y+y=8
4y=8
y=2
so
x=3*y=3*2=6
So the the original number = 10x+y=(10*6)+2=62