you lef out the part of the question that says what the height of the first domino is so I will say it's some x.
first domino is x tall. the next one x × 1.2, third in a row
x × 1.2 × 1.2, 4th in a row x × 1.2 × 1.2 × 1.2
another way of writing the 4th in a row is x × 1.2³
the same applies for the 30th domino which has a height of x × 1.2²⁹ = x × 197.81
if x is 1cm the height of the 30th domino would be 197.81cm which is about the height of a door but for the different values of the first domino (x) you will get different anwsers
hope this helps :)
