Okay, let's see. Karla drove 12,000 miles last year. The question is asking how many gallons of gasoline she would have saved if she had driven a hybrid car that gets 48 miles per gallon instead of her SUV which gets 15 miles per gallon. Hmm, alright. So, I need to figure out the difference in gasoline usage between the two cars over the same distance. 

First, maybe I should calculate how many gallons she used with her SUV. Since her SUV gets 15 miles per gallon, the number of gallons used would be the total miles divided by miles per gallon. So that's 12,000 miles divided by 15 mpg. Let me compute that. 12,000 divided by 15. Let's see, 15 times 800 is 12,000. So, 12,000 ÷ 15 = 800 gallons. Okay, so she used 800 gallons with her SUV.

Now, if she had driven the hybrid car instead, which gets 48 miles per gallon, how many gallons would she have used? That would be 12,000 miles divided by 48 mpg. Let me do that calculation. 12,000 divided by 48. Hmm, 48 times 250 is 12,000, right? Because 48 times 100 is 4,800, 48 times 200 is 9,600, so 48 times 250 is 12,000. So, 12,000 ÷ 48 = 250 gallons. So, she would have used 250 gallons with the hybrid.

To find the savings, subtract the gallons used by the hybrid from the gallons used by the SUV. So, 800 gallons minus 250 gallons equals 550 gallons. Therefore, she would have saved 550 gallons last year. 

Wait, let me double-check the calculations. SUV: 12,000 /15 = 800. Hybrid: 12,000 /48 = 250. 800 -250 =550. Yep, that seems right. The difference in miles per gallon is significant, so the savings should be 550 gallons. 

I don't think I made any mistakes here. The key steps are converting total miles into gallons for both cars and then subtracting the two to get the savings. It's straightforward once you set up the division correctly. Yeah, this should be the correct answer.
Therefore, Karla would have saved $\boxed{550}$ gallons of gasoline.
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