the solution above looks fine, but there is no reason whatsoever to do that much work.

remember, this is DATA SUFFICIENCY, not data solving. you don't have to solve problems once you have ascertained that you CAN solve them.

to this end:

the question prompt tells that the COMBINED RATE for pumps x and y is 1 tank per 48 minutes, or (1/48) tank/min.
notice that this value is the SUM of the individual rates for pump x and pump y; as usual, rates for simultaneous work are additive.

there's no terribly good reason to switch to hours. hours make things easier if you have to solve for actual quantities ... but you don't.

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REPHRASE THE QUESTION:
because the pumps are working for the same amount of time, the amount of water pumped by each is proportional to the pumping rate. therefore, this question can be answered if you can answer either of the following:
what is the rate for pump x?
what is the rate for pump y?

you can also consider this intuitively, without thinking about the proportion: if you know the rates at which two pumps are pumping, and they're pumping for the same amount of time, then you know the fractions of water that come from each. try to imagine (visually) two pumps that are pumping water in a ratio of, say, 2:1, and this should become clear.

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statement (1)
rate x = (1/80) tank/min
sufficient

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statement (2)
rate y = (1/120) tank/min
sufficient

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note that, even if your rephrase of the question was "what are BOTH rates?" - a perfectly good rephrase - you could still find both rates from either one of the individual statements, via subtraction from the combined rate of 1/48.