HI, Kareena!
Okay, so I'm assuming you need to find out how many people fit in a car and how many fit in a van.
Ok, let's let:
X = number of people in a van
Y = number of people in a car
The, we have 2 equations and 2 variables:
2X + 3Y = 21
4X + 1Y = 27
Now, you can multiply the first equation by 2 and then subtract the equations:
2(2X + 3Y = 21) =
4X + 6Y = 42
4X + 6Y = 42
4X + 1Y = 27
----------------
subtract the equations:
5Y = 15
Y = 3
then solve for X:
2X + 9 = 21
2X = 12
X = 6
Therefore:
6 people can fit in a van
3 people can fit in a car