The given question asks us to find the value of y if the highest common factor (HCF) of 210 and 55 can be expressed in the form 210×5 55y. Let's solve this step by step.

Step 1: Determine the prime factors of both numbers
To find the HCF of 210 and 55, we need to determine their prime factors.

Prime factorization of 210:
210 = 2 × 3 × 5 × 7

Prime factorization of 55:
55 = 5 × 11

Step 2: Identify the common prime factors
To find the HCF, we need to identify the common prime factors between 210 and 55. In this case, the only common prime factor is 5.

Step 3: Determine the product of the common prime factors
We need to find the product of the common prime factors, which is 5.

Step 4: Express the HCF in the given form
The HCF of 210 and 55 is 5, which can be expressed as 210×5 55y. Comparing the two expressions, we can see that y should be equal to 1.

Therefore, the value of y is 1.

In conclusion, the value of y is 1 if the HCF of 210 and 55 can be expressed in the form 210×5 55y.