If you can answer "what are you trying to achieve", we may be able to answer your question. If you are simply declaring two initialised variables then:

my $x = "Expected value is";
my $y = 2;
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is the way to do it. However I'd expect $y would cause trouble in your code in that case - you do include use strict; in your script don't you?

If you are trying to increment $y and concatenate the result on to the end of the string then you need something like:

my $x = "Expected value is " . ($y + 2);
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Note that the () are required.