How can I find unknown number between specific numbers? For example I want to find the start with value from following question... How can I do that?

Given Values

Min number=20
Max Number=500
increment number=10
start with=? Needs to be find.
how many times it increments= Always 5
where the cycle stopped now= 205

Conditions;

1. Start with number has to be either 20 or 500 or between 20-500...
2. It always increment 5 times.For example, If the start with number is 75 than numbers goes like First cycle=(75,85,95,105,115) Second cycle=(125,135,145,155,165)... Third cycle (175,185,195,205) and it stops on 205.

Question is: If start with number not known. Is there any way to find it?
29 minutes ago - 4 days left to answer.
Additional Details
my stop number is 205 that way my third cycle stops on 205. When the number stops cycle doesn't need to be 5