Three times as many children as adults attended a concert on Saturday. An adult's ticket cost $7 and child's ticket cost $3. the theater collected a total of $6,000. How many people bought tickets?

3a = c

7a + 3c = 6000

Substitute 3a for c in the second equation and solve for a, then solve for c.

7a+3(3a)=6000

7a+9a=6000
16a=6000
a=375

To solve this problem, we can set up a system of equations to represent the given information.

Let's assume the number of adults who attended the concert is "x". According to the given information, three times as many children attended, so the number of children would be "3x".

We also know that the cost of an adult's ticket is $7 and a child's ticket is $3. Based on this, we can create the equation for the total amount collected:

7x + 3(3x) = 6000

Simplifying this equation will help us find the value of "x" and subsequently the number of attendees.

7x + 9x = 6000
16x = 6000
x = 6000/16
x = 375

So, the number of adults who attended the concert is 375. Since there were three times as many children, the number of children who attended is 3 * 375 = 1125.

Therefore, the total number of people who bought tickets is 375 adults + 1125 children = 1500.