"Scientific Notation" means putting ONLY one non-zero digit in front of the decimal point, and then applying the appropriate exponent to 10 to indicate the magnitude. The exponent shifts "up" for larger values and "don" for smaller values. The specific dimensions are irrelevant.
"Significant Figures" are a different thing, but the use of scientific notation for large and small numbers can also make the proper identification and use of significant figures easier.
(a) 3000000000 ms-1 With no specified decimal point this value actually has only one significant figure. The scientific notation would be
(b) 6400000 m This value actually has two significant figures. The scientific notation would be
(c) 0.0000000016 g This value also has two significant figures. The scientific notation would be
(d) 0.0000548 s This value also has three significant figures. The scientific notation would be