For this case, the first thing we must do is define variables:
x: number of people
y: total cost of the ticket
We write then the linear equation that represents this problem:
y = (- 3/8) x + 42
For y = 30 we have:
30 = (- 3/8) x + 42
We clear the value of x:
(3/8) x = 42 - 30
x = (8/3) * (12)
x = 32
Answer:
the number of people in Marcos's group is:
x = 32
