Area = length*width
length = Area/width
= (9.312*10^4)/(2.56*10^2) = 3.6375*10^2 . . . cm
Selection A is appropriate.
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You already knew that before you even touched your calculator. 10^4/10^2 = 10^2, so only answers A and C should be considered. 9.3/2.6 < 4.5, so only answer A should be considered.
The beauty of scientific notation for numbers is it helps you estimate the result of multiplication and division easily. For many problems, you don't need the actual answer as much as you need the ballpark in which the answer resides.