The cost of hiring a van is partly constant and the other varies with the time spent. It costs 180 for a 2 hours hire and 450 for a 7 hours
c = mt+b
you are given
2m+b = 180
7m+b = 450
Now do what you want with that -- you did not ask a question
C = cost
t = time
C = a + b • t
where
a and b are constants
Substitute the given values in the equation:
a + b • t = C
t = 2 h , C = 180
a + b • t = 180
a + b • 2 = 180
a + 2 b = 180
t = 7 h , C = 450
a + b • t = 450
a + b • 7 = 450
a + 7 b = 450
Now solve system of two equations:
a + 2 b = 180
a + 7 b = 450
The solution is:
a = 72 , b = 54
The cost is:
C = a + b • t
C = 72 + 54 t