You can't add the same number to 2 different numbers and get the same answer, so no.
Answer: 1:5
Step-by-step explanation:
Given: The cost of every mirror is proportional to the cube of the mirror's radius.
i.e. 
Their largest mirrors have radii of 5 meters and their smallest mirrors have radii of 1 meter.
Then,

The ratio of the total cost of 25 of the company's smallest mirrors to the cost of one of the company's largest mirrors will be:

Hence, the ratio of the total cost of 25 of the company's smallest mirrors to the cost of one of the company's largest mirrors = 1:5 .
If you would like to know the bike wheel's diameter in millimeters, you can calculate this using the following steps:
26 inches in diameter
1 inch = 25.4 millimeters
26 inches = 26 * 1 inch = 26 * 25.4 millimeters = 660.4 millimeters
The correct result would be 660.4 millimeters in diameter.
Solution is Y= -12 for your question