So, you're dealing with a unit conversion that must get you from #"cL"#, or centiliters, to #"nL"#, or nanoliters.
One centiliter is equal to #10^(-2)"L"#, and one nanoliter is equal to #10^(-9)"L"#, so you're going from something small to something even smaller. This means that the result must be a bigger number than 35.7, since there are more nanoliters in a liter than there are centiliters in a liter.
You can do this by going to liters first
#"35.7 cL" * ("1 L")/(10^2 "cL") * (10^9"nL")/("1 L") = 35.7 * 10^(7)"nL"#
or by going directly from centiliters to nanoliters
#"35.7 cL" * ("1 nL")/(10^(-7)"cL") = 35.7 * 10^(7)"nL"#
Because 1 liter has #10^2# centiliters and #10^9# nanoliters, one centiliter will have
#"1 cL" * ("1 nL")/(10^(-7)"cL") = 10^7"nL"#
Unit conversions like this one will become a walk in the park once you'll get comfortable with the SI metric prefixes
