Arithmetic operations of rational numbers

A certain electronic component is sold in boxes of 54 for $16.20 and in boxes of 27 for $13.20. A customer who needed only 54 components for a project had to buy 2 boxes of 27 because boxes of 54 were unavailable. Approximately how much more did the customer pay for each component due to the unavailability of the larger boxes.

OG-#125

The only problem I am having with is figuring out the last step.

I found difference and now must solve for 10.2/54. I tried doing long division (which will not work well in a 2 minute time-frame) and then tried breaking up the numerator and denominator. What do you recommend I do for similar questions like this where long division is not optimal and the numbers do not break up easily. I got it down to 17/90 but how am I supposed to know this represents .19?

Thanks