Conversion of Units

Sometimes it is necessary to convert units from one system to another. Units can be treated as algebraic quantities that can cancel each other.
For example, suppose we wish to convert 15.0 in. to centimeters. Here we know that $1in=2.54cm$, so dividing 1in by 2.54cm will gives 1 in result. Applying this conversion we can convert 15in to cm as follows. $$\begin{array} {rcl}15in& = &(15in)(1)\\ 15in& = &(15 in)({2.54 cm \over 1in})\\ & = &(15) (2.54cm) = 38.1cm\end{array}$$ Conversion factors between the SI units and conventional units of length are as follows: