Let \( x \) represent the number of weekdays Lindsay practiced. Given that she practices 30 minutes on each weekday and 50 minutes on Saturday, we can express the total practice time as follows:
- Time practiced on Saturday: 50 minutes
- Time practiced on weekdays: \( 30x \) minutes
The total practice time for the week is:
\[ 30x + 50 = 140 \]
Thus, the equation in the form \( px + q = r \) is:
\[ 30x + 50 = 140 \]
Where:
- \( p = 30 \)
- \( q = 50 \)
- \( r = 140 \)