The Reduced Levels (RLs) of the points P and Q are $+49.600$ m and $+51.870$  respectively. Distance PQ is $20$ m. The distance (in m from P) at which the $+51.000$ m contour cuts the line PQ is

1. $15.00$
2. $12.33$
3. $3.52$
4. $2.27$