cannot convert lambda expression to type bool because it is not a delegate i get the following error someone help me please,

cannot convert lambda expression to type bool because it is not a delegate i get the following error someone help me please,

greater than equal to is >= not =>, that is why you are getting the error.
There are several places in your code where it appears you wanted to use a comparison operator, but flipped the operators. Change
=> to >=
'=>` is the syntax C# uses to specify lamba expressions. So the order you write the operators is important.
Update
Per your comment, the variable vastus3 is not accessible outside of the do statement block. To resolve the error move the declaration up with the others:
int vastus1, vastus2, vastus3;
int vastus3 = int.Parse(tekst1);