Small Engines (Lawn Mowers, etc.): Craftsman Lawn Mower, ok cya, earliest convenience

Question
Yeah I may need a little help. And how much should a oil change cost? I have a lawn mower company willing to fix it and they charged me 57.00 to have it serviced is that too steap?
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Followup To

Question -
I have a push mower a Craftsman Lawn Mower with 4.5 horsepower. I tried to cut the grass on yesterday and the mower started, but it wouldn't stay started. I took off what looked like a filter and it was full of mud,sticky and black. Should this filter be cleaned? How should I go about cleaning it and could this filter be part of why the mower keeps shutting off. Please respond at your earliest convenience. Thanks in advance.

Answer -
Hiya Essence,
Yes- that would be the fuel filter, and it needs replacing.  The gas tank should be flushed as well.
Lemme know if you're unsure about how to do this ok?
CYA

Answer
Hi again Essence (thats such a lovely name)

Hmm - 57.00 IS steep for just an oil change- if they REALLY serviced the mower (new spark plug, new air filter, fuel filter, gas tank flush and oil change)  well- thats not so bad.  AS LONG AS it runs like a top when you get it back.
So..  they did this work for you already?  Or do we still need to flush the tank?