Answer: option b is the correct answer.
Step-by-step explanation:
In a geometric series, the successive terms differ by a common ratio which is determined by dividing a term by the preceding term.
The formula for determining the nth term of a geometric progression is expressed as
Tn = ar^(n - 1)
Where
a represents the first term of the sequence.
r represents the common ratio between successive terms in the sequence.
n represents the number of terms in the sequence.
The formula representing the 4th term of the given sequence would be expressed as
18 = a × r^(4 - 1)
18 = ar^3- - - - - - - - - - - - - - - -1
The formula representing the 6th term of the given sequence would be expressed as
72 = a × r^(6 - 1)
72 = ar^5- - - - - - - - - - - - - - - -2
Dividing equation 2 by equation 1, it becomes
4 = r^(5 - 3)
2² = r^2
r = 2
Substituting r = 2 into equation 1, it becomes
18 = a × 2^3
18 = 8a
a = 18/8 = 2.25
