Sonia and Ravi drive one round of the field at the same point, same time and same direction.
So, they will meet again after LCM of both values at the starting point.
To get the LCM we have factorize the number.
Factor of 18=2×3×3
Factor of 12=2×2×3
LCM =2×2×3×3=36
Hence, they will meet together at the starting point after 36 minutes.