On plotting the diagram of given data we get,

Let Q(h,0)
∵OP reflected by x+y=1
So, the image of Q lies on y=3x
∴1x−h=1y=2−2(h−1)
⇒x=1,y=1−h
Since it lies on y=3x
∴1−h=31
⇒h=1−31=33−1
On rationalising the numerator we get,
⇒h=33−1×3+13+1
⇒h=3+32