We know that,
If two objects are moving at speeds S1 and S2, their relative speed is
S1 + S2, if they are moving in opposite direction and
S1 – S2, if they are moving in the same direction.
Time is taken to meet/catch =Initial distance separating them/ (Relative Speed i.e. S1 ∓ S2)
Car A starts at 9:00 am & Car B starts at 10:00 am
By 10:00 am car A already travels (30 x 1)= 30 km.
So, by 10:00 am The distance between car A and car B is (180 - 30) = 150 km.
∴ Time taken to meet = 150 / (30 + 20)
= 3 hrs.
Car A and Car B will meet at (10 + 3)= 13 i.e at 1:00 pm.