# How many "nanometres" in 7.5*mum?

$7500$ $n m$
$1$ $\mu m$ $=$ $1 \times {10}^{-} 6 m$
$1$ $n m$ $=$ $1 \times {10}^{-} 9 m$
$7.5 \cdot \mu m = 7.50 \times {10}^{-} 6 m \times {10}^{9} n m \cdot {m}^{-} 1$ $=$ $7500 \cdot n m$.