Let's denote the cost of each pair of shorts as \( x \).
Sophie is buying 3 outfits, which means she is buying 3 shirts and 3 pairs of shorts.
The cost for the shirts is: \[ 3 \text{ shirts} \times 10 \text{ dollars per shirt} = 30 \text{ dollars} \]
Let’s express the total cost of the shorts. Since she is buying 3 pairs of shorts, the cost for the shorts is: \[ 3 \text{ pairs of shorts} \times x \text{ dollars per pair} = 3x \text{ dollars} \]
Now we can set up the equation for the total cost: \[ 30 + 3x = 64.50 \]
Next, we can solve for \( x \) by first subtracting 30 from both sides: \[ 3x = 64.50 - 30 \] \[ 3x = 34.50 \]
Now, divide both sides by 3 to find \( x \): \[ x = \frac{34.50}{3} = 11.50 \]
Thus, each pair of shorts costs $11.50.