To find the cost of a pair of pants, we first need to determine what 130% of the cost of the pair of shorts is.
The cost of a pair of shorts is $15.
Now, we calculate 130% of $15:
\[ 130% \text{ of } 15 = \frac{130}{100} \times 15 = 1.3 \times 15 = 19.5 \]
So, the cost of one pair of pants is $19.50.
Now, to find the cost of 3 pairs of pants, we multiply the cost of one pair of pants by 3:
\[ 3 \text{ pairs of pants} = 3 \times 19.5 = 58.5 \]
Thus, the cost of 3 pairs of pants is
\[ \text{$} 58.50 \]
So, the final answer is:
\[ \boxed{58.50} \]