Question on microeconomics

[FishNDip]

Hello, So I'm not sure if this is the right place to ask this, but I'm doing Microeconomics and I'm trying to find Marginal Cost. The formula Modern States gives me is  MC=(TC2-TC1)/(Q2-Q1) They tell me to fill out MC and I do it, but I'm getting 0.25 for the first answer instead of 1.25 and 0.5 for the second answer instead of 2.5. (Please view attachment for more info.)



Confused, I go looked up a khan Academy Video,
https://www.khanacademy.org/economics-fi...total-cost

I use the Formula Modern States gives me, and bingo! It works there, however I keep getting the wrong answers on Modern States.
Is Modern States wrong? Am I doing something wrong? Thanks for the help!