If the track error is 8° and the heading change is 12°, the closing angle must be 4° (the heading change is always equal to the sum of the track error and the closing angle). Since 8 is two times 4, the distance to intercept will be two times the distance flown (the interior angles of a triangle are always in the same proportion as the opposite sides). You will regain track in twice the distance you have flown (and twice the time).

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Thanks very much sir