Let the 4-passenger cars be represented with F
Let the 6-passenger cars be represented with S
Rocket Coaster has 15 cars
So that F + S = 15 ----- Equation 1
Also, we were told that the total room for 72 passenger
so that 4F + 6S = 72 ----- Equation 2
Solving the two equations simultaneously using the substitution method,
Step 1
From equation 1:
Make F the subject of the formula
F = 15 - S ---- Equation 3
Step 2
substitute equation 3 into equation 2
4 (15 - S) + 6S = 72
Step 3
60 - 4S + 6S = 72
6S - 4S = 72 - 60
2S = 12
divide both sides by 2
S = 12/ 2
S= 6
Step 4
Substitute the value of S = 6 into equation 3
F = 15 - 6
F = 9
So the number of 4-passenger cars = 9
the number of 6-passenger cars = 6