What ratio is equivalent to 21/27 with lower terms

7/9 because if you simplify 21/27 you have to divide it by something that can go into both equally, which in this case is 3

This is basically just asking you to simplify the ratio/fraction.
To simplify it, find the highest number that can go into both numbers and divide both sides by it. This number is called the greatest common factor (GCF).

The first step to finding the GCF is listing all of the factors for both numbers.
Factors for 21:
1, 3, 7, and 21
Factors of 27:
1, 3, 9, 27
Greatest Common Factor (GCF):
The highest number that these sets have in common is 3, so this is the GCF.

Now that you know the GCF, divide both sides of the fraction/ratio by it.
21 / 3 = 7
27 / 3 = 9
Simplified ratio/fraction: 7/9 or 7:9

7/9, also written as 7:9 in ratio form, is the simplest form of 21/27.