To write \( 3.9 \times 10^1 \) in standard form, you need to perform the multiplication.
Calculating \( 3.9 \times 10^1 \):
- \( 10^1 = 10 \)
- Multiply \( 3.9 \) by \( 10 \):
\[ 3.9 \times 10 = 39 \]
So, the standard form of \( 3.9 \times 10^1 \) is \( 39 \).