Lindsay practices the guitar 50 minutes on Saturday and 30 minutes on most weekdays. Last week she practiced 140 minutes. How many weekdays did she practice? Write an equation in the form px+q=r to represent this problem.
Let x be the number of weekdays Lindsay practiced.
Then the number of minutes Lindsay practiced on weekdays is 30x.
The number of minutes Lindsay practiced in total is 30x + 50.
So 30x + 50 = 140.
Therefore, the equation is 30x + 50 = 140. Answer: \boxed{30x + 50 = 140}.