Number of tiles in blue ring = 6
Number of tiles in yellow ring = 12
Number of tiles in blue ring = 18
Observe the terms, they are forming an Arithmetic series as each term is 6 more than the previous term. We are to find the number of tiles in 30th ring, which will be the 30th term of the A.P.
So,
30th term of AP = 1st term +(30 - 1) x Common Difference
30th term of AP = 6 + 29 x 6 = 180
Thus, there will be 180 tiles in the 30th ring of white tiles