"x 2.54", inside the printf() format area - that's the part between the " ", is not where it belongs.
Do the calculation before the printf() statement, just like I showed you (twice now).
You CAN do calculations in a printf() statement, but NOT where you have the x 2.54, currently. Just a bit more clear to do it on it's own line of code, just before the printf() statement.
You have your work cut out for you -- study hard and long.