First, let's calculate \( \frac{1}{2} \) of 14:
\[ \frac{1}{2} \times 14 = 7 \]
Next, we need to find what percent \( 7 \) is of \( 70 \). We can express this as an equation:
\[ \text{percent} = \left( \frac{7}{70} \right) \times 100 \]
Calculating \( \frac{7}{70} \):
\[ \frac{7}{70} = \frac{1}{10} = 0.1 \]
Now, converting to percent:
\[ 0.1 \times 100 = 10 \]
Thus, \( 7 \) is \( 10% \) of \( 70 \). Therefore, the missing number in the box is:
\[ \boxed{10} \]