To find out how much 15 pens will cost, we first need to determine the price per pen.
Miguel bought 8 pens for $3.84. So, the price per pen is calculated as follows:
\[ \text{Price per pen} = \frac{\text{Total cost}}{\text{Number of pens}} = \frac{3.84}{8} = 0.48 \]
Now that we know each pen costs $0.48, we can calculate the cost for 15 pens:
\[ \text{Cost of 15 pens} = \text{Price per pen} \times \text{Number of pens} = 0.48 \times 15 \]
Calculating that:
\[ 0.48 \times 15 = 7.20 \]
Therefore, the cost of 15 pens will be $7.20.