It's a proportion.
2 is to x as 15 is to 9, or 2/x = 15/9.
Multiply the means and extremes
15x = 18
divide both sides by 15 to get x by itself.
x = 1.2
Answer:
that would be the third one 12 ft, 12 ft, 20 ft because the lengths of 12+12 have enough to reach the 20 length compared to 30+30 which would only equal 60 and no more making it a line.
To find the common ratio
divide by the previous numb/number beside it:

so
It would be false because 879 will be rounded up to 880 or 900.